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Fresh install of dos 6.22, unfortunately there appears to be a virus in MBR, each time I get Virus:DOS/V_Sign when re-using floppy from this machine. I can't connect HDD to modern PC, any idea how I can get rid of it?

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  • How do you know you have this particular virus? – user722 Nov 22 '20 at 22:51
  • I was transfering files on floppy to 386, forgot to set write protection, used the same disk again and it was picked up by windows defender – Bartek Malysz Nov 24 '20 at 9:22
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If you have a clean MS-DOS 6.22 installation disk, you can boot from that, then run MSAV from your hard drive — the antivirus included with MS-DOS, a repackaged version of Central Point’s product, can detect and clean up V-Sign (which it identified as “Sigalit”).

You could also use any other DOS-era antivirus program capable of cleaning V-Sign, such as F-Prot. If you can get the target PC on the Internet, download it directly there, otherwise you’ll have to download it on another system and transfer it. Don’t forget the definition file too; you won’t be able to get that from F-Prot any more, but you’ll find the last updates on SAC: fp-def.zip and macrdef2.zip (you can also download the program itself from SAC, it’s fp-316f.zip — this will be useful when the main site disappears, now that F-Prot has been shut down).

Whichever antivirus you use, you will have to run it on all the disks (including floppies) on the DOS PC. Ideally you should copy and run the antivirus after booting from a clean floppy, but it might be difficult to prepare one (you’d need another PC capable of writing floppies).

With F-Prot you’ll need to specify the /OLD flag on the command line, otherwise it will complain that the signatures are too old.

As suggested by Joshua, booting a DOS installation disk and running FDISK /MBR will also get rid of the virus on the hard drive. That leaves the floppy disks to clean up — SYS A: would take care of bootable floppies, any others would still need their boot sector rewritten.

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    F-Prot was the second best antivirus on MS-DOS I came into contact with ... However IIRC it did not fit onto floppy The best one did (was faster and smaller however discontinued much sooner so there is a chance it will not know that particular virus) it was called TBAV and of coarse the worst one was AVG from any aspect ... – Spektre Nov 23 '20 at 8:33
  • Ah yes, TBAV... And no, F-Prot doesn’t fit on a floppy; I’ll clarify what I meant in the answer. – Stephen Kitt Nov 23 '20 at 9:11
  • fdisk /mbr from the boot media usually clobbers boot viruses. – Joshua Jun 10 at 19:41
  • Indeed, thanks @Joshua — that only leaves floppies to take care of. – Stephen Kitt Jun 10 at 20:58
  • For floppies, to kill boot sector viruses, copy the files off and FORMAT. That at least is obvious. – Joshua Jun 10 at 23:00

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