When the virus is in memory, it hooks INT 21h to infect any DOS executable that is run by writing itself to the end the file. It also hooks FindFirst/Next DOS calls (DIR command), and infects the files that are accessed by this call. Not every file would be infected.
The virus behaves stealthy so that no size change can be observed on infected file, but it does on those uninfected. It subtracts the infection size from all files, making the size of uninfected files to have smaller file size, an underflow occurs on files smaller than the virus itself.
EDIT.COM 413 bytes SYS.COM 9,432 bytes GOAT.COM 10,000 bytes
After infection and the virus stays memory:
EDIT.COM 64,944 bytes (uninfected) SYS.COM 9,432 bytes (infected) GOAT.COM 8,995 bytes (uninfected)
The displayed size of an uninfected file plus infection size minus original size is always equal to 65,536, in case there is a size underflow.
The exact memory usage is 1,040 bytes.
On the 13th of any month, the virus corrupts hard drive sectors, during this process it would generate some creepy noise from the hard drive. It also displays the following in the screen corners and hangs the system:
H A T E
The system might load properly after this, but the user might encounter unexpected errors on program runtime.
The virus contains the internal text strings: