The general principle behind it is so stupid it doesn't bare thinking about.
Firstly, the heat wouldn't destroy all the virus. All the **** they spoon-feed you about AIDS is complete crap. They'll tell you all this crap about it not surviving the cooling process used for donated blood and how it won't survive in open air and it's all crap. Granted, some of the blood itself would be burned to a cinder, but enough would survive with active virii in it to be dangerous.
But then there's the small fact that the blood would have to land on open cuts to infect people. And even then, the body's immune system would attack and kill the majority of the foreign blood and the virus along with it. If 500 people were bathed in blood, mayb 50 would become infected.
Put simply, it's vastly more complicated than a nail-bomb and about 1/10 as effective.
They'd be better off sending 50 people out with the flu to ride buses all day and create en epidemic. It's certainly kill a few hundred old people and it'd cripple the economy for weeks.