The Frodo virus is one of the most advanced "stealth" viruses, and is
quite successful in hiding from detection. If it is active in memory and
you look at the directory, the virus will show you the original length of
any infected program. In addition, it will intercept most attempts to
read infected files, so only the original, non-infected file will be seen.
If CHKDSK is run while the virus is active, it will often detect an
inconsistency in the number of disk blocks allocated to infected files,
and their apparent length.
Frodo activates on Sept. 22. when it may attempt to place a Trojan on boot
sectors. This Trojan will display the message "FRODO LIVES" in large
letters on the screen, surrounded by a moving pattern. The code to write
the Trojan to the disk seems to be garbled in all known versions of the
virus and will probably "hang" the computer.