Hacked Blog?

Ok, I downloaded Heat Theme v4 from somewhere.
now once in awhile there are new posts in my blog that I didn't post! Is it that the nuller of the script left him/herself a backdoor to post at will?
I guess I should know better and just buy the theme witch I already did by the way.
I just want to know if anyone else has seen this happen?

If you're the administrator you should be able to log-in the front door of the blog and delete the posts. Login to the backdoor and try changing your administrator password. I have never had this happen to me, but it's a good idea to change your password whenever you suspect a hacker.

That's exactly what I did, I went into admin and deleted the post also changed the pass to a more difficult one,
few days later the post was back on!
this time I went into admin and simply edited the link they had put on the post, no body has modified it so far.