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This topic is similar to this one:

Help Me Decide - What's the best on-demand virus scanner?

But I think that when it comes to on-demand scanners - the more, the better. But ONLY if the DO NOT integrate into system in any way, so you don't have to uninstall them (Avira PC Cleaner, Malwarebytes, Symantec Norton Power Eraser, ESET Online Scanner...), such as Microsoft Safety Scanner, ClaimWin, Herdprotect, Zemana - those are fully portable and no need to be installed in any way... I wan't them all :D!

BTW is there some kind of a list of all existing on-demand scanners?