Pretoria overwrites the first 879 bytes of infected files with itself, and stores the original 879 bytes at the end of the file. This makes it impossible to fully restore programs shorter than 879 bytes, as their original length is not stored anywhere.
When an infected program is executed, the virus searches the entire current directory for .COM files to infect. As it uses a full-depth recursive directory search, this may take considerable time on an XT-class machine.
On June 16th the execution of an infected file will cause all entries in the root directory to be changed to 'ZAPPED'. June 16th is the day when the Soweto riots first broke out.
The virus uses a simple substitution encryption.