Security breached

Apologies to anyone who read and was offended by a comment that someone left at today.
I just logged on to check the site statistics and found a couple of new comments had been posted. Now I know there are lots of you out there who look at, but we don’t get many comments (HINT! HINT!). So I went to check the comments and found one of them was just a list of URLs to sites offering to enlarge bits of me that I have no interest in enlarging. (Well I didn’t actually check the sites to see what they were offering but from the urls I guessed what the content would be.)
It was bad enough that the comment had been left and it has now been deleted. What concerned me was that the whole entry body had been replaced with similar URLs. I don’t know how someone could do this. I thought I had taken all the recommended security precautions when I installed Moveable Type but still someone snuck through.
This has concerned me since I set up this site. I am now advertising my address and obviously makes it a target for hackers. Needless to say I will be discussing this with my hosting service and see what else I can do.
In the meantime, I’ll just keep chekcing and try to remove stuff like this as soon as possible after it is posted.