Torrent Sites

while reading through a thread i read a reference to torrent sites in relation to free software etc. Also on the same thread i read a reference to them being dangerous(viruses etc) im wondering what the dangers are and would i be doing somthing illegal if i was to download and use material from a torrent site(s) i googled and found many sites but no information as to whether its illegal or safe to use such sites/material. I sincerly appologise if im out of line but my thirst for learning begs me to ask this question.