Seriously, the purveyors of malware must be rubbing their hands together waiting for April because they know oodles of users will stick with XP. They'll have any number of zero day exploits waiting to be unleashed and every XP system will be vulnerable in perpetuity.
Exactly !
If I were a malware writer, sure I'd continue releasing a few scraps here and there. But I'd be holding off my best work until April, both because I'd know I'd be able to charge a premium rate on the black market, and also because there would be bugger all Microsoft would ever do about it.
Seriously, do not underestimate the malware writers.