======== Newsgroups: alt.comp.virus Subject: Frequently Asked Questions 4/4 From: harley@europa.lif.icnet.uk (David Harley) Date: 22 Mar 1996 16:04:08 GMT alt.comp.virus (Frequently Asked Questions) ******************************************* Version 1.01c : Part 4 of 4 Last-modified 21st March 1996 ("`-''-/").___..--''"`-._ `6_ 6 ) `-. ( ).`-.__.`) (_Y_.)' ._ ) `._ `. ``-..-' _..`--'_..-_/ /--'_.' ,' (il),-'' (li),' ((!.-' ADMINISTRIVIA ============= Disclaimer ---------- This document is an honest attempt to help individuals with computer virus-related problems and queries. It can *not* be regarded as being in any sense authoritative, and has no legal standing. The authors accept no responsibility for errors or omissions, or for any ill effects resulting from the use of any information contained in this document. Not all the views expressed in this document are mine, and those views which *are* mine are not necessarily shared by my employer. Copyright Notice ---------------- Copyright on all contributions to this FAQ remains with the authors and all rights are reserved. It may, however, be freely distributed and quoted - accurately, and with due credit. B-) It may not be reproduced for profit or distributed in part or as a whole with any product for which a charge is made, except with the prior permission of the copyright holders. To obtain such permission, please contact the maintainer of the FAQ. David Harley ************ -------------------------------------------------------------------------- TABLE OF CONTENTS ***************** Part 1 ------ (1) I have a virus - what do I do? (2) Minimal glossary (3) What is a virus (Trojan, Worm)? (4) How do viruses work? (5) How do viruses spread? (6) How can I avoid infection? (7) How does antivirus software work? Part 2 ------ (8) What's the best anti-virus software (and where do I get it)? (9) Where can I get further information? (10) Does anyone know about * Mac viruses? * UNIX viruses? * macro viruses? * the AOLgold virus? * the xyz PC virus? (11) Is it true that...? (12) Favourite myths * DOS file attributes protect executable files from infection * I'm safe from viruses because I don't use bulletin boards/shareware/Public Domain software * FDISK /MBR fixes boot sector viruses * Write-protecting suspect floppies stops infection * The write-protect tab always stops a disk write * I can infect my system by running DIR on an infected disk Part 3 ------ (13) What are the legal implications of computer viruses? -----> Part 4 ------ -----> (14) Miscellaneous -----> Are there anti-virus packages which check zipped files? -----> What's the genb/genp virus? -----> Where do I get VCL and an assembler, & what's the password? -----> Send me a virus. -----> Is it viruses, virii or what? -----> Where is alt.comp.virus archived? -----> What about firewalls? -----> Viruses on CD-ROM. -----> Removing viruses. -----> Can't viruses sometimes be useful? -----> Do I have a virus, and how do I know? -----> What should be on a (clean) boot disk? -----> What other tools might I need? -----> What are rescue disks? -----> Are there CMOS viruses? -----> How do I know I'm FTP-ing 'good' software? -----> What is 386SPART.PAR? -----> Can I get a virus to test my antivirus package with? -----> When I do DIR | MORE I see a couple of files with funny names... -----> Reasons NOT to use FDISK /MBR -----> Placeholders ------------------------------------------------------------------- (14) Miscellaneous ================== Are there anti-virus packages which check zipped files? ------------------------------------------------------- An increasing number of packages seem to support checking .ZIP and other compression formats on the fly. DSAVTK, AVP and NAV 3.0/NAV95 support some formats. The number of formats supported may become as big a selling point as the total number of viruses detected, but for most of us it's only really an issue if we do a lot of scanning of CDs, for instance. Even then, it becomes urgent only if you *unpack* the archive and want to run programs. Compilers of CDs, however, are *not* entitled to use this as an excuse for not scanning their collections. What's the genb/genp virus? --------------------------- This is McAfee-ese for "You may have an unrecognised ('generic') boot-sector (genb) or partition-sector (genp) virus". Re-check with a more recent version or the latest version of another reputable package. Where do I get VCL and an assembler, & what's the password? ----------------------------------------------------------- Wrong FAQ. You don't learn anything about viruses, programming or anything else from virus toolkits. You want rec.knitting. B-) I can't believe there's anyone left on the Internet who doesn't know the VCL password, but I'm not going to tell you anyway. OK, maybe you want an assembler to learn assembly-language, not just to rehash prefabricated code. Where do you get TASM? You buy it from Borland or one of their agents, either stand-alone or with one of their high-level languages. If you want freeware or shareware, I guess you can still get the likes of CHASM and A86 (SimTel mirror sites in SimTel/asm). Send me a virus --------------- Anti-virus researchers don't usually share viruses with people they can't trust. Pro-virus types are often unresponsive to freeloaders. And why would you *trust* someone who's prepared to mail you a virus, bona-fide or otherwise? [A high percentage of the 'viruses' available over the internet are non-replicating junk.] Requests for viruses by people 'writing a new anti-virus utility' are usually not taken too seriously. * We get rather a lot of such requests, which leads to a certain amount of cynicism. * Writing a utility to detect a single virus is one thing: writing a usable, stable, reasonably fast scanner which detects all known viruses is a considerable undertaking. There are highly experienced and qualified people working more or less full time on adding routines to do this to antivirus packages which are already mature, and unless you have a distinctly novel approach, you don't have much chance of keeping up with them. * It may be that the research you're interested in has already been done. Say what sort of information you're looking for, and someone may be able to help. * You can't afford to use junk 'viruses' for research, and the best collections are largely in the hands of people who won't allow access to them to anyone without cast-iron credentials. If you want to test anti-virus software with live viruses, this is *not* the way to get good virus samples. Valid testing of antivirus software requires a lot of time, care and thought and a valid virus test-set. Virus simulators are unhelpful in this context: a scanner which reports a virus when it finds one of these is actually false-alarming, which isn't necessarily what you want from a scanner. Read Vesselin Bontchev's paper on maintaining a virus library: ftp://ftp.informatik.uni-hamburg.de/pub/virus/texts/viruses/virlib.zip It said in a review.... ----------------------- Reviews in the general computing press are rarely useful. Most journalists don't have the resources or the knowledge to match the quality of the reviews available in specialist periodicals like Virus Bulletin or Secure Computing. Of course, it's possible to produce a useful, if limited assessment of a package without using live viruses based on good knowledge of the issues involved (whether the package is NCSA-certified, for instance): unfortunately, most journalists are unaware of how little they know and have a vested interest in giving the impression that they know much more than they do. Even more knowledgeable writers may not make clear the criteria applied in their review. Is it viruses, virii or what? ----------------------------- The Latin root of virus has no plural form. Since the use of the word virus is borrowed from biology, you might like to conform to the usage normally favoured by biologists, doctors etc., which is viruses. However, a number of people favour the terms virii/viri, either to avoid confusion with the biological phenomenon (but what's the point of distinguishing in the plural but not in the singular?), or to avoid being mistaken for anti-virus researchers..... Where is alt.comp.virus archived? --------------------------------- It isn't, as far as anyone seems to know. No-one currently working on the FAQ is likely to offer archiving, since a full archive would include uploaded viruses. When the FAQ is established, I may do some work on making an occasional digest available. What about firewalls? --------------------- Firewalls don't generally screen computer viruses. However, there are currently two products that scan for viruses at a point either before or after a "normal" firewall to the Internet (or internally between post offices.) These products can scan incoming and outgoing E-mail attachments for viruses. MIMESweeper, by Integralis, uses your favorite scanner (e.g. F-PROT, Thunderbyte, Dr. Solomon's, Sophos, etc) for scanning the viruses after it has opened up the E-Mail attachments in a secure area on the hard drive of the NT machine. The use of a "batch" file allows the scanning to use any switches or commands that are available to the scanner program(s) and also allows multiple scanners to be used with different switches, etc. which it runs. If clean, it sends the E-Mail on. Files which it cannot scan are 'quarantined' in the secure area to be scanned 'by hand'. MIMESweeper ver. 2.1 reads MIME attachments, UUENCODE, and recognises ZIP and recursive .ZIP archives, OLE, but does not yet read many other compression or binary encoding formats. (CDA, BinHex, LHA and Stuffit are expected shortly). It runs under NT Workstation and requires, as minimum, a 486 with 24Mb RAM, 500Mb hard disk, and a CD-ROM drive (for installation only). It works with cc:Mail, SMTP with MIME attachments, Microsoft Mail, or MHS, and is said to be usable as a filter for other material as well as file viruses such as trojans. (MIMEsweeper will be adding FTP and HTTP later). [The following is included because Integralis' Sales Dept. in the UK don't seem to have caught up with vs. 2.1 yet.] MIMESweeper vs. 1.0 reads MIME attachments and recognises ZIP archives, but does not read other compression formats or binary encoding formats such as uuencode. Trend's InterScan VirusWall is similar to MIMEsweeper but uses Trend's own scanning engine only as the scanner. Trend also scans FTP traffic. Trend currently runs on SUN Solaris 2.4-5 and will be adding NT later. These products do real scanning before the mail hits the hard drive but, at least until the holes are filled in the above products, make sure your mail attachments, WWW downloads etc. can't be automatically executed and use a good TSR/VXD in combination with a good scanner. Note that scanning FTP traffic is likely to add a heavy network overhead and probably won't catch as many viruses as checking *all* files from *all* sources with a desktop scanner For firewall-related information, see comp.security, comp.security.firewalls, or, if you don't mind your mail by the ton, the firewalls mailing-lists. Books: Firewalls and Internet Security (Cheswick, Bellovin) - Addison-Wesley Building Internet Firewalls (Chapman, Zwicky) - O'Reilly Viruses on CD-ROM ----------------- Viruses have been distributed on CD ROM (for instance, Microsoft shipped Concept, the first (in the wild) macro virus, on a CD ROM called "Windows 95 Software Compatability Test" in 1995). It is wise to scan CD ROMs on arrival for viruses, just like floppies. If the CD ROM has compressed or archived files it is wise to scan it with an anti-virus package which can cope with large amounts of compressed and archived files. [If you scan all drives at every boot, though, you may find that this gives you a good incentive to remove CDs from your CD drive before you power down, especially if your scanner isn't set to allow you to break out of a scan. B-)] Removing viruses ---------------- It is always better from a security point of view to replace infected files with clean, uninfected copies. However, in some circumstances this is not convenient. For example, if an entire network were infected with a fast-infecting file virus then it may be a lot quicker to run a quick repair with a reliable anti-virus product than to find clean, backup copies of the files. It should also be realised that clean backups are not available. If a site has been hit by Nomenklatura, for example, it may take a long time before it is realised that you have been infected. By that time the data in backups has been seriously compromised. There are virtually no circumstances under which you should need to reformat a hard disk, however: in general, this is an attempt to treat the symptom instead of the cause. Likewise re-partitioning with FDISK. If you use a generic low-level format program, i.e. one which isn't specifically for the make and model of drive you actually own, you stand a good chance of trashing the drive more thoroughly than any virus yet discovered. Can't viruses sometimes be useful? ---------------------------------- Vesselin Bontchev wrote a respected paper on this subject: ftp://ftp.informatik.uni-hamburg.de/pub/virus/texts/viruses/goodvir.zip Fred Cohen has done some heavy-duty writing in the other direction. Start with "A Short Course on Computer Viruses", "It's Alive!"(Wiley). In general, it's hard to imagine a situation where (e.g.) a maintenance virus is the *only* option. I have yet to see a convincing example of a potentially useful virus which *needs* to be a virus. Such a program would have to be *much* better written and error-trapped than viruses usually are. Do I have a virus, and how do I know? ------------------------------------- Almost anything odd a computer may do can (and has been) blamed on a computer "virus," especially if no other explanation can readily be found. In most cases, when an anti-virus program is then run, no virus is found. A computer virus can cause unusual screen displays, or messages - but most don't do that. A virus may slow the operation of the computer - but many times that doesn't happen. Even longer disk activity, or strange hardware behavior can be caused by legitimate software, harmless "prank" programs, or by hardware faults. A virus may cause a drive to be accessed unexpectedly (and the drive light to go on) - but legitimate programs can do that also. One usually reliable indicator of a virus infection is a change in the length of executable (*.com/*.exe) files, a change in their content, or a change in their file date/time in the Directory listing. But some viruses don't infect files, and some of those which do can avoid showing changes they've made to files, especially if they're active in RAM. Another common indication of a virus infection is a change to interrupt vectors or the reassignment of system resources. Unaccounted use of memory or a reduction in the amount normally shown for the system may be significant. In short, observing "something funny" and blaming it on a computer virus is less productive than scanning regularly for potential viruses, and not scanning, because "everything is running OK" is equally inadvisable. What should be on a (clean) boot disk? -------------------------------------- To make an emergency bootable floppy disk, FORMAT A: /S with a disk in A> which is the proper "density" for the drive. I'd suggest you also COPY these commands from C:\DOS to it: ATTRIB, CHKDSK (or SCANDISK if you have DOS6), FDISK, FORMAT, SYS, and BACKUP and RESTORE (or whatever backup program you use, if it will fit). They may come in handy if you can't access the hard disk, or it won't boot up. The boot disk should have been created with the same version of DOS as you have on your hard disk. It should also include any drivers necessary to access your hard disk and other devices. If you become virus-infected it can be very helpful to have backup of your hard disk's boot sector and partition sector (also known as MBR). Other useful tools to include are a small DOS-based text editor (for editing AUTOEXEC.BAT, CONFIG.SYS and so forth), a copy of the DOS commands COMP or FC (for comparing files), FDISK and SYS (make sure they are from the same version of DOS as you are booting). There is a school of thought that your boot disk should also include your anti-virus software. The problem with this is that anti-virus software should be updated frequently, and you may forget to update your boot disk each time. Ideally you will have been sent a clean, write-protected copy of the latest version of your anti-virus software by your anti-virus vendor. If you want to use the DOS program EDIT, remember that you need both EDIT.* and QBASIC.* on the same disk. What other tools might I need? ------------------------------ Other suggestions have included a sector editor, and Norton Utilities components such as Disk Doctor (NDD). These are not suitable for use by the technically-challenged - any tool which can manipulate disks at a low-level is potentially dangerous. If you do use tools like this, make sure they're good quality and up-to-date. If you attack a 1Gb disk with a package that thinks 32Mb is the maximum for a partition and MFM disk controllers are leading edge, you're in for trouble.... A copy of PKZIP/PKUNZIP or similar compression/decompression utility may be useful both for retrieving data and for cleaning (some) stealth viruses. The MSD diagnostic tool supplied with recent versions of DOS and Windows is a useful addition. QEMM includes a useful diagnostic tool called Manifest. Heavy duty diagnostic packages like CheckIt! may be of use. There are some useful shareware/freeware diagnostic packages, too. Obviously, these are not all going to go on one bootdisk. When you prepare a toolkit like this, make sure *all* the disks are write-protected! Tech support types are likely to find that an assortment of bootable disks including various versions of DOS comes in useful on occasion. If you have one or two non-Microsoft DOS versions (DR-DOS/Novell DOS or PC-DOS), they can be a useful addition. DoubleSpaced or similar drives will need DOS 6.x; Stacked drives will need appropriate drivers loaded. What are rescue disks? ---------------------- Many antivirus and disk repair utilities can make up a (usually bootable) rescue disk for a specific system. This needs a certain amount of care and maintenance, especially if you make up more than one of these for a single PC with more than one utility. Make sure you update *all* your rescue disks when you make a significant change, and that you understand what a rescue disk does and how it does it before you try to use it. Don't try to use a rescue disk made up on one PC on another PC, unless you're very sure of what you're doing: you may lose data. Are there CMOS viruses? ----------------------- Although a virus (e.g. antiCMOS) CAN write to (and corrupt) a PC's CMOS memory, it can NOT "hide" there. The CMOS memory used for system information (and backed up by battery power) is not "addressable," and requires Input/Output ("I/O") instructions to be usable. Data stored there are not loaded from there and executed, so virus code written to CMOS memory would still need to infect an executable program in order to load and execute whatever it wrote. A virus could use CMOS memory to store part of its code, and some tamper with the CMOS Setup's values. However, executable code stored there must first be first moved to DOS memory in order to be executed. Therefore, a virus can NOT spread from, or be hidden in CMOS memory. [There are also reports of a trojanized AMI BIOS - this is not a virus, but a 'joke' program which does not replicate. If the date is 13th of November, it stops the bootup process and plays 'Happy Birthday' through the PC speaker. In this case, the only cure is a new BIOS - contact your dealer.] [There are also reports of a trojanized 3rd-party keyboard which puts the string 'Welcome to Datacomp' to the console, if I can use such archaic terminology in a Mac context B-) - both the Virus-L FAQ versions include information on this.] How do I know I'm FTP-ing 'good' software? ------------------------------------------ Reputable sites like SimTel and Garbo check uploaded utilities for viruses before making them publicly available. However, it makes sense not to take anything for granted. I'm aware of at least one instance of a virus-infected file being found on a SimTel mirror: you can't scan a newly-uploaded file for a virus your scanner doesn't know about. Good A/V packages include self-checking code, though it's unsafe to depend even on this 100%. Be paranoid: you know it makes sense.... In general, don't run *anything* downloaded from the Internet, BBSs etc. until it's been checked with at least one reputable and up-to-date antivirus scanner. What is 386SPART.PAR? --------------------- People are sometimes alarmed at finding they have a hidden file with this name. It is, in fact, created by Windows 3.x when you configure it to use a permanent swap file (a way of allowing Windows to work as if you had more memory than you really do. On no account should you delete it, as it will upset your configuration. If you wish to remove it or adjust the size, do so via the 386 Enhanced setting in Control Panel. However, a permanent swap file usually improves performance on a machine with relatively little memory. The file is not executable as such, and reports of virus infection are usually false positives. Can I get a virus to test my antivirus package with? ---------------------------------------------------- Well, I won't send you one... Most packages have some means of allowing you to trigger a test alert. There is a standard EICAR test file which is recognized by F-Prot and Dr. Solomon's AntiVirus ToolKit, and possibly other antivirus packages. Type or copy/paste the following text into a file called EICAR.COM, or TEST.COM or whatever. X5O!P%@AP[4\PZX54(P^)7CC)7}$EICAR-STANDARD-ANTIVIRUS-TEST-FILE!$H+H* Running the file displays the text EICAR-STANDARD-ANTIVIRUS-TEST-FILE. Scanning the file with one of the components of these packages should trigger an alert. There has been a long thread recently on whether the Rosenthal Simulator is useful for this sort of job. This will be considered at length here when I have the time to look at it, but it should be noted that many of the anti-virus researchers who have contributed to this document have expressed considerable scepticism. When I do DIR | MORE I see a couple of files with funny names... ---------------------------------------------------------------- Actually, this is in the Virus-L FAQ. Read that and post the question to comp.virus or alt.comp.virus if you're still worried. Basically, the answer is that MORE creates a couple of temporary files, being considerably less efficient than the Unix utility it attempts to emulate. Most versions of DOS since the Middle Ages support the syntax DIR /P, which does the same job less messily. In fact, if you have a version of DOS later than 5, you might consider incorporating it into the environment variable DIRCMD, so that it becomes your default on directory listings which exceed 1 screenful. Of course, other utilities such as ATTRIB can also be filtered through MORE like this, which may result in similar symptoms. ------------------------------------------------------------ Reasons NOT to use FDISK /MBR ----------------------------- See Section 12 in part 2 of this FAQ for further information about FDISK with the undocumented /MBR switch. However, people with virus problems are frequently advised, out of ignorance or maliciousness, to use this switch in circumstances where it can lead to an inability to access your disk drive and possible loss of data (not to mention hair and sanity). Essentially, you should avoid using FDISK /MBR unless you have it on good authority that it's safe and necessary to do so. In most circumstances, it's safer to clean a partition sector with a good anti-virus program. You should avoid FDISK /MBR at all costs under the following circumstances: 1. Under an infection of viruses that don't preserve the Partition Table e.g., Monkey, reported at 7.2% of the infections reported to _Virus Bulletin_ for December '95, the last report for which I have data 2. Under an infection that encrypts data on the hard drive and keeps the key in the MBR, e.g, One_half -- reported at 0.8% worldwide 3. When security software, e.g., PC-DACS is in use 4. When a driver like Disk Manager or EZDrive is installed 5. When a controller that stores data in (0,0,1) is in use 6. When more than one BSI virus is active, in some conditions 7. When a data diddler is active, e.g. Ripper, accountable for 3.8% of the infections reported in the study cited above (N.B.: while this case won't be fixed by AV utilities, at least one will know why there are problems with the drive) Placeholders ------------ [How do I know I have a clean boot disk?] I made some exhaustive notes on this a few months back. Can I find them now? No. Will I write them up again? Sometime.... The Virus-L FAQ includes some relevant info, though. [Problems with PC disks in macs and vice versa)] An altogether expanded Mac section could be quite nice. [nomenclature] This merits lots of discussion. However, life may be too short... ------------------------------------------------------------ End of a.c.v. FAQ Part 4 of 4