An industrial strength magnet might make the data on the drives unreadable, if you mean the kind they use to lift cars in a scrapyard. The drives are pretty well protected from even strong permanent magnets. The NSA recommendation is to reduce them to fine dust in a grinder following degaussing since there is concern that even massive magnetic noise may be insufficient to hide everything. But you will not be able to use them for anything else after zapping them with a degausser. Aside from the damage to the mechanical parts and circuits, the platters themselves are factory formatted (like a "blank" CD) and if you erase that level of formatting via degaussing, you will not be able to format them for use under an OS.
https://www.kjmagnetics.com/blog.asp?p=hard-drive-destruction Throwing away your drives is almost certainly overkill for any common virus. If you are not confident that your antivirus software can detect and remove suspected viruses, then the DBAN followed by fresh format is as far as you probably need to go. Modern hard drives have a firmware secure erase routine built in, but it is difficult to access from most OS's, and even blocked by some BIOS versions to prevent the accidental erasure of the drive. One way of calling the routine is here:
http://cmrr.ucsd.edu/people/Hughes/secure-erase.html. Not for the faint of heart, but it does not require a second computer and once the sequence is initiated it is impervious to any interference by a program running on the computer.
That stuff applies mostly to destroying classified data. As far as removing a virus, like any other computer program, all you need to do is make a few bits unreadable to make it stop working. You do not have to remove all traces from the possibility of forensic recovery by state actors. A simple delete will kill it dead.