I Owe is a dangerous memory resident parasitic virus on MS-DOS. It infects only the IO.SYS file. While infecting the virus scans the header of IO.SYS for the area that contains only the zero bytes, and writes itself into there, if such area exist.

While loading from infected system the virus copies itself into the video memory, hooks INT 1Ah, waits for DOS loading, then it hooks INT 21h and overwrites C:\IO.SYS on first call to DOS functions. Then the virus removes itself from the memory.

The infection method is very unusual one, and it may halt the system. The virus can spread only while loading from infected floppy disk, and it infects only IO.SYS on C: drive. The virus contains the text strings:


Info from Secure List.

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