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Could there be a reason why an employee would access your site on a regular basis on non-Google-business matters? Have you tracked what page(s) this person visits?
Personal visits from Google always seem to raise alarm bells, but it could be just that - a personal visit.
It would seem that someone on the AdSense Team is checking something to do with your site, and I am guessing that there will be some members here checking their logs to see if they have any referrals from gnome.corp.google.com too.
GNOME Office is a meta-project, with the mission to coordinate productivity applications for the GNOME Desktop. We intend to produce a productivity suite composed of entirely free software.......
Taking into account the geeky origins of Google, I would not be surprised if the makers of the Google Adsense monitoring portion of the program created a system based on this architecture, which leaves a telltale sign as a referrer in our logs.
I would not be too worried... if you are a high earner? high volume? particular topic? or just happen to throw up some kind of flag.... you might get the visit. You can only do something about things that you have control over. Just make sure that those are covered and chances are you will be fine.
So keep your stuff fair and as long as Google Team can see a lot of impressions and a normal CTR, they would never be bothered. But suddenly if your CTR rises above a certain level, their red lights seem to get on!