Junk in my Technorati tags and sometimes body

I have not worked on my blog in some time.. but tonight when I went to do so, I found a lot of junk in previous posts technorati tags.. and in some cases the entire blog text was gone and it was now filled with trash.. spam I guess.. a lot of stuff about ringtones and the like.

How did this happen.. and how can I resolve it/fix it/preclude it from happening again?

I just upgraded to 2.5.1 but the problem was there before I upgraded.

Thanks for any advice/suggestions.

Tom