infolinks injection – site hacked

Hi,

We are using a genesis child theme on the latest wp. All plugins, theme files and core are up to date. We are constantly being hacked and infolinks being injected into the site – small snippets of javascript that introduce the infolinks are being placed in theme files randomly it seems.

Has anyone else experienced anything like this that may be able to give us some idea how to stop it short of disabling all plugins and building the system up from scratch one plugin at a time. The theme is believed solid as a premium theme from studiopress.

Any information or advice most welcome.

Thanks.