When the virus is in memory, it first infects C:\COMMAND.COM, then it hooks INT 21h to infect any DOS executable file that is run by writing itself to the end of the file.
Not every file would be infected by the virus, and it does not infect files that are smaller than or equal to 1,000 bytes.
Files infected by the virus might not function properly or even cause a system crash.
The exact memory usage is 720 bytes.
On January 21, when the virus is in memory, on running any program the virus decrypts and displays the message, followed by beeps:
Virus GISELA 2.0 By EJECUTOR (Hecho en Argentina) Feliz cumpleaños Gisela.
Translation (from Spanish):
Virus GISELA 2.0 By EJECUTOR (Made in Argentina) Happy birthday Gisela.
The virus contains the internal text string: