unfortunately this happened to you
unfortunately you are not the only one
this topic was discussed here in the forum already in extenso
7 of my pages have been hacked in the last time (not Pixelpost... )
this happens because of old insecure scripts, wrong server configuration to name a few

you can find some answers in our wiki, look for the chapter "security" and here in the forum as well

if you are into php and scripting, you will find a lot of websites around as well, do a search for "mysql injection, hacking, Cross-Site-Scripting etc."

I am sure with the new version you will be safer