A Quick Question!

I'm still fairly new to blogging so I was wondering if anyone else has this happening. I have e-mail alerts set so I know if anyone comments on an older post. For the last week or so I have been getting anonymous comments,always on older post never on the most recent. The odd thing is that this person sounds like Simon Cowell,judging my blog. Then at other times it is just a bunch of jibberish. Has this happened to any of you? If so,what or who is it?