Looks like I’m not the only one who has a virus at the moment. The trusty old Osborne ended up with what appeared to be an MBR or boot-sector infection, and the Sound Blaster 16 installation disks I’d been using were also detected as infected. I originally assumed the disks had infected the PC, although without a known-clean copy from before they entered the Osborne, it’s just as possible the machine infected the disks.

I only discovered the problem after using the disks in the Osborne and then bringing them back to another machine to reformat and re-image. So a big thanks to Avast under Windows XP for sounding the alarm, and to Caluser2000 over at the Vintage Computer forums for pointing me towards a DOS-era cleanup tool.

F-PROT 3.16f saved the day. The scan report identified ABCD.A in the master boot sector. The archive I used was fprot_dos_316f.zip, with virus definitions dating into 2009. F-PROT 3.16f was the final DOS version and is perfectly at home on a 486.

For this sort of boot-sector cleanup, you really want to start the infected computer from known-clean media rather than letting the compromised hard disk boot. Ideally the rescue floppy should be write-protected too, so the infected machine can’t modify it. Windows 95 is now installed as well, and the next challenge is getting this thing onto the internet to some degree.

Sources