Blackhole exploit problems

I have a blog running using the free WordPress blog tool provided by my host Hostmonster. Yesterday, my blog was infected by the Blackhole Exploit virus. My host, Hostmonster, is absolutely no help whatsoever in fixing the problem even though I do not own the code or even know how to access the code. (nor can they assure me it won’t happen again?!)

Can someone please point me in the direction as to how to remove the virus?

Thank you.