It is not a dangerous(?) memory resident parasitic virus. It copies itself to Interrupt Vectors Table, hooks INT 21h and writes itself to the end of COM files (except COMMAND.COM) that are closed. While infecting a file the virus uses not documented DOS calls and System File Tables.
When files are executed the virus scans the command line for "doom" text. If it is found, the virus modifies the i386 register CR0 - it sets on the reserved bit (CR0 OR 40000000h). The virus also reverses that bit when any program is executed.
The virus contains the text strings:
doom
VM
DOOM MD! R.ShuHard 1997
