Is DOS under Unix immune?

[Thomas Hoberg]

I recently caught a case of Jerusalem-B on my 386 DOS/UNIX box running
vanilla DOS and a 'nice' new little game. Since for some reason I can
not access the hard disks when I boot DOS off a floppy disk (some weird
DOS-BIOS interaction here) VPIX sure came handy as a way to examine
the DOS partitions and the reproduction characteristics of the virus
without risking further infection. I mounted the DOS partitions
read-only and used UNIX tools (find and fgrep) to locate infected files
after I had found a substring identifying the virus. I then logged in as
super-user and zapped the infected files, which wasn't too careful...
Quitting VPIX infected QUIT.COM on the UNIX-filesystem (which can't do
any harm--installing the virus is the last thing that DOS task does).

I'd say DOS under UNIX can aid somewhat when investigating a virus, but
if you use DOS partitions viruses can do anything DOS can do: Whereas
you might be protected from those viruses that twiddle the hardware,
plenty of damaged can still be done. Running VPIX off a unix file system
will give you somewhat more security, depending on the amount of effort
you are willing to put into file permissions.