These are dangerous memory resident parasitic viruses. They hook INT 21h and writes itself to the end of .COM files that are executed.
Jackel.654
Depending on the system time it beeps by internal system speaker and halts PC. It contains the strings:
DH
_àcKèL
Jackel.713
It copies itself to the memory at the address 8000:0100, and does not fix MCB list. It might halt PC. While infecting this virus disables some anti-virus monitors like TBSCAN and VSAFE. It deletes the files:
TI-VIR.DAT
CHKLIST.CPS
*._??
SCANVAL.VAL
It also contains the text string:
_àcKèL5Version 5.0a
