I'm not a computer geek by any means. I asked about worms or whatever simply because I don't know what terms may be applicable to the Mac.
I use Firefox because I prefer it to Safari. I'll look into the add-ons you mentioned, though.
It could be the wireless connection. I'm staying with family and the connection is theirs, so I don't know. They don't seem to be having any problems (even if they are on PC's).