These are dangerous memory resident parasitic viruses. They hook INT 21h and write themselves to the end of .COM- and .EXE-files that are executed. They infect some files incorrectly, these files halt the system on execution. Depending on the system time these viruses also hook INT 08h and delay on each timer tick. They contain the internal text strings:
"Cholera.a": Cholera v1.0 by dr Hellraiser 94-02-03
"Cholera.b": Cholera v2.0 by dr Fleischman 93-12-29
