Stupid, or Do Nothing, is a DOS file virus from 1989. Both the original and its variants are poorly written and may cause the system to hang, along with many other problems.
When a file infected with Stupid is run, the Stupid virus becomes resident. It copies itself to 9800:100h in memory, and therefore may not work on systems with less than 640 kilobytes of memory. It scans the current directory and infects the first .com file it finds. The virus has no way of telling if a file is already infected, and may reinfect a file multiple times.
The virus does not protect the memory it allocates for itself. It is possible and even very likely that the virus will be overwritten in memory and will therefore be unable to infect any further.
It contains the text "Stupid 1989 Virushmock!".
Stupid.Sadam is 919 bytes long. The virus infects .com files as they are executed. It sometimes decrypts the files and displays this text: "HEY SADDAM LEAVE QUIETLY BEFORE I COME". This variant may cause an "Insufficient memory" message when a .bat file is run. If COMMAND.com has been infected with this variant, the system will fail to boot. Running some programs may produce an I/O error. Some DOS commands, including "DIR" may not function properly and the system will often hang requiring a reboot.
Stupid.Sadam may have originated in Israel from the same creator. However, it was first reported in France in 1990 September and isolated in Israel in 1991 January.
Stupid.Profesor is also 919 bytes long, but contains the text "The Professor is in town again !!!". It may allocate unusually large amounts of memory for itself, causing some programs to fail. It infects two .com files in the current directory. Executing an infected program may result in strings of meaningless characters to be displayed.
Virus analysts considered this virus to be poorly written and not a threat. It was discovered on an Israeli BBS.
Yuval Tal. Reports collected and collated by PC-Virus Index, Computer Virus Catalog 1.2: "Do Nothing" Virus. 1990.02.15
F-Secure Antivirus, F-Secure Virus Descriptions : Stupid.
Patricia Hoffman. VSUM, Do-Nothing Virus.
-. -, Saddam Virus.