Virus.DOS.PS-MPC.Yam.1136 is a memory resident parasitic encrypted virus on DOS. The virus is named by the name of the creator YAM (Youths Against McAfee), however it also has an unofficial alias of MathTest.


When the virus is in memory, it hooks INT 21h to infect any executable file that is run.

The virus contains bugs that can hang the system during infection.

Advanced details

The TSR memory usage is 2,384 bytes.

MD5 hash:



The virus activates in between 9:00am and 10:00am.

If the virus is already in memory, on running an infected program it shows a math question, the user must answer it in order to run the host.

It's time for a math test curtesy of YAM!
And the question is...
What is (a math question)

If the user answered it correctly, the host program will run afterwards. Otherwise it displays the following and returns to DOS instead:


See also