HPS is a polymorphic Windows 95 virus which contains this text:
< Hantavirus Pulmonary Syndrome (HPS) Virus BioCoded by GriYo / 29A >
Once detected, the F-Secure security product will automatically disinfect the suspect file by either deleting it or renaming it.
HPS stays active in memory and infects Win32 EXE files as they are accessed, encrypting its own code with variable polymorphic encryption layer.
HPS activates on Saturdays. If a non-compressed Windows bitmap (BMP) file has been opened, the virus horizontally flips the picture. HPS patches the value DEADBABE (in hex) to the end of the bitmap header area to avoid flipping the same image again. Since non-compressed bitmap files are frequently used by Windows 95 and 98, this causes all kinds of weird effects - such as the start-up and power-down screen of Windows being "mirrorized".
See also: Marburg
Technical Details: Peter Szor, F-Secure, 1997