Security vulnerability questions

I just had a problem with my website that has all the trappings of a successful hack [it has happened before    ]  My traffic usage skyrocketed in a short period of time. 

See http://picasaweb.google.com/JamesMelhui … 5557846850

The last time this happened, it was a vulnerability in Coppermine Photo Gallery.  I removed this application for now, and had transitioned the whole website to a new virtual private server (VPS).  (Run by the company Fluidhosting).   Now it has happened again, but I am not an experienced enough in internet security, Linux, Apache, etc.  My web host says they are looking into it, but haven't yet heard what they have found.

The only "application" on the website was PunBB (1.2.17).  I have just upgraded to 1.2.20.  Everything else was static html files. 

My log files show a sustained attack somewhere before 17 August and successful on the 18th.  I wish I knew of some way to better monitor the VPS.  I probably need to learn more about internet security.  Anyway, they got root access...

Was the security breach likely to be through 1.2.17, and if so, is there anything saved in the mysql database about it?  Or should I not worry and trust in 1.2.20 until the next release?

Thanks for any ideas.

James