a freeform mmo with an economy like EVE might be able to swing user-created viruses with user-manufactured cures...
Not to say it couldn't be made to work, but I highly suspect it'd just result in a pandemic that perma-deaths the player base. Could be handy if you could dope a capsuleer with a debuff though, like a stim with no upside. (Maybe pay off an NPC corp for the subterfuge?)