Someone Posted Affilate links in my footer - need to get shot of them quick

[grifter]

Hi

I just noticed two new users registered - this is for guest writing options - and there is two affiliate links in my footer where it says powered by wordpress, it actually says:

Powered by Aweber Wordpress Plugin and Passive Income.

And both go to affiliate looking sites with opt in pop ups.

Firstly - can I find out if one of these users done this
Secondly - if not how did this get inserted here and how can I prevent it

My users register with contributor rights, is this too much, would this allow them to play about with the settings?

If so would author let them post only (with pre-approval of course)

Also checked at bottom of user profile for new user and all these are ticked:

Enable Genesis Admin Menu
Enable SEO Settings Submenu
Enable Import/Export Submenu

Thanks