XM/Compat.A is a polymorphic macro virus. The virus changes its appearance so it looks different in every infected file. This is done by inserting random comments into the virus code.
Disinfection & Removal
The virus consists of 11 subroutines: Auto_Open, Auto_Close, Auto_Exit, Auto_Help, Macro1, Macro2, Macro3, Macro4, Macro5, Macro6, and Macro7. They are in one module which has polymorphic name.
The virus puts the following comment in the beginning of its code:
Macro recorded (month)/(day)/(year) by (user)
The variables (month), (day), (year) and (user) are different for every environment and replication. The virus saves its code in different files and paths depending on the environment.
On Macintosh, the files are "Office 97 Compatibility" and "MS Excel Visual Basic Example", but on Windows 95 they are "Off97com.xla" and "Vba_xl.txt".
The virus builds its code as Add-In in Off97com.xla file. Compat works only in Excel 95. It does not infect Excel 97.
Compat has a payload which activates after 31 August 1998. After that date, the virus modifies the contents of random cells by changing the values slightly. This can have disasterous effects.