Userpics Album Hacked

[scrapgranny]

I have just been notified by my server that my gallery has been hacked and used for a bank fraud scam. My photos seem to all be gone. What the heck happened here? How can I fix it? Can I get my photos back? AND the big question....How does this happen and how can it be prevented?

[Nibbler]

A link to your gallery would help.