IM spam...

Lately, I've been getting AIM spam at least two times per IM session. I'm not quite sure what to do; do I change my SN? I know one way is to simply ignore the IM's, but the problem is that sometimes the names are like "Sara468", and as I know about ten Sara's, I figure someone got AIM or changed their SN. Or it'll be so distinct that I'll think it could be a spammer, but won't know for sure - after all, there have been two instances where I nearly ignored someone, assuming it was a spammer, and it ended up being a friend who simply chose a SN like "lovergirl54" without realizing that anyone they IMed would think they were a pornsite spammer.