Firon, about my issue, I found out what's going on. I opened Task Manager and forced a recheck, and this is what happened: CPU usage of utorrent.exe kept steady at 0~4%, so did the memory usage, at 13MB. However as the check was progressing, the "Physical Memory" field on Task Manager's window kept increasing until it reached 93% (I have 6GB of DDR3@1666Mhz), and then Windows got extremely slow. When I stopped the check, the slowness was gone and Physical Memory went to 15%. So there must be a memory leak somewhere in the check process. Strange thing the memory used by utorrent.exe didn't increase. (Memory: Private Working Set).