Originally posted here by politroyx
For me, the most deadly virus is when the creator of the virus doesn't even know how to create the antidote for the virus he made.
Presently I think most viruses can't survive a reformat/reinstall... save the old ones that did nasty things like reset "unbreakable" passwords (eg. an old Apple virus that turned an expensive printer in to an equally expensive paperweight by setting its normally unset "usage" password - the "I forgot my password" solution was to buy a new printer).