F-PROT version 2.17 - March 1995

The F-PROT anti-virus package contains a
virus scanner combined with a disinfection
program, as well as a resident monitoring
program for intercepting known viruses.

This program is free of charge for private
users, but others are required to register
or obtain the 'Professional' version - see
the documentation for details.

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 checksuming
program, which detects changes to files or boot secors, 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".

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 not use heuristics with "All files" selected,
and doing so will produce a warning message.