Spammers using Moderators/Administrator accounts to Edit Old Posts

[Erika]

Hi -

I was wondering if anyone else has ever had this problem. Today I logged onto my site to find that one of my moderator and one of administrators accounts had been hacked. Over 2,000 older posts on my site made by these 2 staff members had been edited to insert spam links that appear under their original post like this:

________
Body Science

Does anyone know where I can begin to correct this problem? I've told everyone on staff they should change their passwords immediately, but other than that, I've got no idea where to begin??? I'm running VB 3.7.4

In addition, it looks as though some of these edits do appear in the moderator logs, but only a very few of them. I've banned all the IP addresses that made the changes from the few mod log entries that I can see. All of the IP's look like proxies.

Any suggestions?