Best course to take, to delete 1000's of spam thread?
 

I haven't used my forums in a long time. It's in active, but I wish to leave it open for archiving purposes. HOwever, I been away for so long that, it has filled up with spam. How do I go about deleting these spam? I have a dedicated mysql server, but for some odd reason I can not delete more than 40 threads at time. (Time out error) If I manually delete all the threads, I expect this to take weeks.