A few years back I was researching a problem I was having on my computer and I ran across some advice that recommended running Spybot and Adaware and one other free malware removal program (that i can't remember). The logic being some programs would catch what the others miss... and so to be sure you are clean you could run all 3 of these programs. This was recommended as a low-tech kind of solution... a sort of idiot-proof catch all.

Is this ok to do... and really necessary?