If it happens to be the 11th November when the infected program is run, or if the encryption seed is AEh, the beginning of the current program file is overwritten by a 194 byte long program. Normally, when the infected file is run, a dummy critical error handler is installed during the infection stage and the virus tries to infect one EXE file in the current directory and one EXE file in the subdirectories of the root directory. Files which are hidden or read-only are not infected. The file attribute is cleared and restored afterwards if infection did not succeed. On successful infection only the archive bit is restored, and the hidden and read-only attributes are set so as to prevent multiple infection.
Infection is done by rounding up the length of the file to the next paragraph and appending.