Cruncher is an unordinary virus; it stays resident in memory and infects files normally, when they are executed. In addition to this, it finally applies a self-extracting packing layer on the infected files, packing both the original code and the appended virus code.
This makes the virus more difficult to detect, especially since the packing code is stolen from the freeware DIET packer, which is similar to LZEXE and PKLITE. For this reason, several antivirus programs have had a false alarm of Cruncher in clean DIET-packed programs.
Cruncher is also the only known virus which actually saves disk space, since infected programs are usually decreased in size by 20-40%.
There are two known variants of Cruncher, V1.0 infects COM files and V2.0 infects EXE files.
Cruncher was written in 1993 by 'Masud Khafir' of the TridenT virus group.
F-Secure anti-virus products might detect Cruncher-infected files as 'possibly a DIET-packed dropper of Coffeeshop'.
Depending on the settings of your F-Secure security product, it will either automatically delete, quarantine or rename the suspect file, or ask you for a desired action.
More information on the scanning and removal options available in your F-Secure product can be found in the Help Center.
You may also refer to the Knowledge Base on the F-Secure Community site for more information.