During execution of an infected file the virus decrypts itself by using 5 different decryptors. However, it is not polymorphic. The virus uses several anti-debugging tricks like using INT 1,3,9 as decryptors and direct port commands.
After that it hooks INT 13h, 21h and stays memory resident. BatMan_II.3372 is a stealth virus, it changes the DOS file time stamp to 62 seconds. During execution the virus searches for *.EXE files, then writes itself to the end of them.
Once detected, the F-Secure security product will automatically disinfect the suspect file by either deleting it or renaming it.
BatMan_II sometimes corrupts files, due to a bug in it's infection routine. The corrupted files halt or reboot the system and they will not work after the disinfection either.
The virus contains a few text strings, but they are encrypted:
Bat Man II *.EXE COMMAND \NAWIAT ( --> backwards \TAIWAN )
The virus has shorter variants, too.
BatMan_II was found in the wild in USA in August 1996.
Technical Details: Peter Szor, F-Secure, 1996