Heuristic analysis

Scanning for viruses by using search strings is not the ultimate solution
to the virus problem.  If using an up-to-date scanner (or better yet, two
scanners from different companies), one can be fairly certain that all
known viruses will be detected.  The scanners may or may not detect new
variants which have been created by modifying older viruses, but if a new
virus is written entirely from scratch, it will probably not be detected by
any existing search string.

The virus may be detected by a generic monitoring program when it
activates - perhaps when trying to perform some suspicious action, such as
reformatting the hard disk.  It may also be detected by a checksumming
program, which detects changes to files or boot sectors, after they have
been infected.  Nevertheless, it is preferable to try to detect the
presence of the virus without actually running a virus-infected program.

The heuristic analysis is basically a small expert-system, which has a set
of rules describing viruses, and attempts to apply them to the programs it
analyses.  It is still only in an experimental stage and is not flawless -
some viruses cannot yet be detected in this way, and an occasional false
alarm is to be expected.

Currently a few programs are known to cause a false positive, including:

  Any program protected with the HyperLOCK encryptor ... not surprising, 
  considering that it claims that "Attemping to reverse engineer this
  software may result in data loss".

  Any program protected with the PROTECT encryptor.

  A few heavily "armored" programs, that use multiple layers of
  anti-debugging techniques.  XTG.EXE (Xtree Gold) is one example.

  RXINTMGR.COM

  Some files belonging to Central-Point's PC-Tools.   

In addition, if the heuristics report a non-executable file as suspicious,
it is almost certainly a false alarm - the heuristics are only intended to
analyse executable files, and will not produce meaningful results if used
on a data files.  You should NEVER use heuristics with "All files" selected,
and doing so will produce a warning message.

Experienced users may wish to run the heuristic scan with the /PARANOID
switch on - HOWEVER, THIS WILL SIGNIFICANTLY INCREASE THE RISK OF FALSE
ALARMS, so use it with care.

We are not interested in receiving copies of false alarms that are only
reported with /PARANOID, so don't waste your time sending them to us.