Firefox only took like 1%, uTorrent took 300MB. After closing them, it didn't help, that svchost had still the whole 11GB.

Btw, I have 2x2GB and 2x4GB dual channel RAM. But the hardware is not the issue. Like I said, this happens only from time to time, perhaps even less than once a month, but I have to mention that my PC is running 24/7, restarting it sometimes definitely solves the problem, if existing. Nothing to worry about, just would like to know which svchost it is.