v by ames-io.ARPA with INTERNET ; Tue, 9 Feb 88 16:33:19 PST Received: Tue, 9 Feb 88 16:22:52 PST by ames.arc.nasa.gov (5.58/1.2) Date: Tue, 9 Feb 88 16:22:52 PST From: Valentin R. Perez Message-Id: <8802100022.AA05128@ames.arc.nasa.gov> To: alzulman%sat.decnet@ames-io.arpa, douglas%sat.decnet@ames-io.arpa, mhansen%sat.decnet@ames-io.arpa, wiedman%ear.decnet@ames-io.arpa, wilkinson%sat.decnet@ames-io.arpa Subject: Virus Update From ARPANET Digest! TO: Consultants FROM: Valentin R. Perez RE: Virus Update From ARPANET! DATE: February 9, 1988 Subject: Another PC Virus Issue 74 of the Info-IBMPC digest contained a description of a "virus" discovered at Lehigh University which destroys the contents of disks after propagating itself to other disks four times. Some of us here in Israel, never far behind other countries in new achievements (good or bad), are suffering from what appears to be a local strain of the virus. Since it may have spread to other countries (or, for all we know, may have been im- ported from abroad), I thought it would be a good idea to spread the word around. Our version, instead of inhabiting only COMMAND.COM, can infect any ex- ecutable file. It works in two stages: When you execute an infected EXE or COM file the first time after booting, the virus captures interrupt 21h and inserts its own code. After this has been done, whenever any EXE file is executed, the virus code is written to the end of that file, increasing its size by 1808 bytes. COM files are also affected, but the 1808 bytes are written to the beginning of the file, another 5 bytes (the string "MsDos") are written to the end, and this extension occurs only once. The disease manifests itself in at least three ways: (1) Because of this continual increase in the size of EXE files, such programs eventually be- come too large to be loaded into memory or there is insufficient room on the disk for further extension. (2) After a certain interval of time (apparently 30 minutes after infection of memory), delays are inserted so that execution of programs slows down considerably. (The speed seems to be reduced by a factor of 5 on ordinary PCs, but by a smaller factor on faster models.) (3) After memory has been infected on a Friday the 13th (the next such date being May 13, 1988), any COM or EXE file which is executed on that date gets deleted. Moreover, it may be that other files are also af- fected on that date; I'm still checking this out. (If this is correct, then use of Norton's UnErase or some similar utility to restore files which are erased on that date will not be sufficient.) Note that this virus infects even read-only files, that it does not change the date and time of the files which it infects, and that while the virus cannot infect a write-protected diskette, you get no clue that an at- tempt has been made by a "Write protect error" message since the pos- sibility of writing is checked before an actual attempt to write is made. It is possible that the whole thing might not have been discovered in time were it not for the fact that when the virus code is present, an EXE file is increased in size *every* time it is executed. This enlargement of EXE files on each execution is apparently a bug; probably the intention was that it should grow only once, as with COM files, and it is fortunate that the continual growth of the EXE files enabled us to discover the virus much sooner than otherwise. From the above it follows that you can fairly easily detect whether your files have become infected. Simply choose one of your EXE files (preferably your most frequently executed one), note its length, and ex- ecute it twice. If it does not grow, it is not infected by this virus. If it does, the present file is infected, and so, probably, are some of your other files. (Another way of detecting this virus is to look for the string "sUMsDos" in bytes 4-10 of COM files or about 1800 bytes before the end of EXE files; however, this method is less reliable since the string can be altered without attenuating the virus.) If any of you have heard of this virus in your area, please let me know; perhaps it is an import after all. (Please specify dates; ours was noticed on Dec. 24 but presumably first infected our disks much earlier.) Fortunately, both an "antidote" and a "vaccine" have been developed for this virus. The first program cures already infected files by removing the virus code, while the second (a RAM-resident program) prevents future in- fection of memory and displays a message when there is any attempt to in- fect it. One such pair of programs was written primarily by Yuval Rakavy, a student in our Computer Science Dept. In their present form these two programs are specific to this particular virus; they will not help with any other, and of course, the author of the present virus may develop a mutant against which these two programs will be ineffective. On the other hand, it is to the credit of our people that they were able to come up with the above two programs within a relatively short time. My original intention was to put this software on some server so that it could be available to all free of charge. However, the powers that be have decreed that it may not be distributed outside our university except under special circumstances, for example that an epidemic of this virus actually exists at the requesting site and that a formal request is sent to our head of computer security by the management of the institution. Incidentally, long before the appearance of this virus, I had been using a software equivalent of a write-protect tab, i.e. a program to prevent writing onto a hard disk, especially when testing new software. It is called PROTECT, was written by Tom Kihlken, and appeared in the Jan. 13, 1987 issue of PC Magazine; a slightly amended version was submitted to the Info-IBMPC library. Though I originally had my doubts, it turned out that it is effective against this virus, although it wouldn't be too hard to develop a virus or Trojan horse for which this would not be true. (By the way, I notice in Issue 3 of the digest, which I received only this morning, that the version of PROTECT.ASM in the Info-IBMPC library has been replaced by another version submitted by R. Kleinrensing. However, in one respect the new version seems to be inferior: one should *not* write-protect all drives above C: because that might prevent you from writing to a RAMdisk or an auxiliary diskette drive.) Of course, this is only the beginning. We can expect to see many new viruses both here and abroad. In fact, two others have already been dis- covered here. In both cases the target date is April 1. One affects only COM files, while the other affects only EXE files. What they do on that date is to display a "Ha ha" message and lock up, forcing you to cold boot. Moreover (at least in the EXE version), there is also a lockup one hour after infection of memory on any day on which you use the default date of 1-1-80. (These viruses may actually be older than the above-described virus, but simply weren't noticed earlier since they extend files only once.) The author of the above-mentioned anti-viral software has now extended his programs to combat these two viruses as well. At present, he is con- centrating his efforts on developing broad-spectrum programs, i.e. programs capable of detecting a wide variety of viruses. Just now (this will give you an idea of the speed at which developments are proceeding here) I received notice of the existence of an anti-viral program written by someone else, which "checks executable files and reports whether they include code which performs absolute writes to disk, disk for- matting, writes to disk without updating the FAT, etc." (I haven't yet received the program itself.) Y. Radai Computation Center Hebrew University of Jerusalem RADAI1@HBUNOS.BITNET ------------------------------ Subject: Virus (Trojan) protection program now available from SIMTEL20 Now available via standard anonymous FTP from SIMTEL20... Filename Type Bytes CRC Directory PD1: FLUSHOT2.ARC.1 BINARY 5539 AFA8H Here are some comments from the author, Ross Greenberg: There exists a low-level form of dirt who gets joy out of destroying your work. They release a program, typically called a 'Trojan Horse', which is designed to erase or otherwise damage your disks. The programs are released into the public domain and typically are downloaded or distributed exactly as you may have received this file. Once run, they would print some sort of self-congratulatory message and proceed to erase your data. Obviously, these type of programs are Not A Good Thing, and should be avoided. However, usually you'll only know you've been bit by a trojan after the fact. Recently, a new breed has been developed. Called a 'virus', it infects all disks that it sees with a copy of itself, and then each of these copies are capable of infecting all disks that *they* see. Eventually, at some predetermined instance (a date, a time, a certain number of copy operations), the virus attacks and destroys whatever disks it can. By this time, though, the virus has spread, and a friends' machine may also be infected, infecting the disks of their friends and so forth. It was to counter just such a program that the enclosed program, called FLU_SHOT, was developed. The current virus making the rounds infects the command processing program called "COMMAND.COM". Every bootable DOS disk must have a copy of this file. FLU_SHOT examines each write and will not allow a write operation to the COMMAND.COM file to take place without your permission. Normally, there should never be a write operation to this file, so it should be effective in that regard. To run FLU_SHOT, place a copy of it in your root directory on the disk you boot your system from. Additionally, a line to invoke FLU_SHOT should be placed in your AUTOEXEC.BAT file. If you find the virus attacking your disk, please try to preserve a copy of it and to forward it to me at my BBS at (212)-889-6438. Once I have a copy of the virus, I should be able to develop another program which would serve as a vaccine. Please be aware that there is a possibility that, if FLU_SHOT determines a write operation taking place to your COMMAND.COM, it *may* be a legitimate one ---- check the currently running program. FLU_SHOT may indicate that a TSR program you're running seems to be causing a problem. If this happens to you, and you're sure the TSR you're running is a valid one, then merely place the FLU_SHOT invokation line in your AUTOEXEC *after* the TSR invokation line. Additionally, FLU_SHOT can not determine whether your current COMMAND.COM is infected, only if a COMMAND.COM is about to be infected. The odds of you being hit with this virus are slim, but running FLU_SHOT should keep this particular incarnation of the virus from infecting your disks. Ross M. Greenberg (212)-889-6438 24hr BBS, 2400/1200,N,8,1 ----- Note from Keith: This program is legitimate. Ross is a personal friend whose programming skills I highly respect. --Keith Petersen Arpa: W8SDZ@SIMTEL20.ARPA Uucp: {decwrl,harvard,lll-crg,ucbvax,uunet,uw-beaver}!simtel20.arpa!w8sdz GEnie: W8SDZ ------------------------------