These are memory resident parasitic viruses. They hook INT 9, 21h and write themselves to the end of .COM and .EXE files that are executed or opened. They overwrite the first 16 bytes of .COM files with Jmp-Virus routine. At the end of infected file there is the string "EDCL".
Tim.1600.a
This is very dangerous virus. It does not infect the BACKUP.COM file. It also hooks INT 13h, and depending on the number of the keys that are pressed, disables a writing to the disk (INT 13h, AH=3). It contains the enciphered texts:
Hi to Eastern Digital. Greetings to Mister L.Megafuck to Mihai Sirbu -- MicroTimSoft.
COMEXEBACKUP.COM
Tim.1600.b
This virus is not a dangerous one, it just displays the message:
+-----------------------------------------------+
¦ ¦
¦ MegaFuck from Eastern Digital ¦
¦ ¦
+-----------------------------------------------+
