Referring Keywords are Numbers for MSN - in Google Analytics

[dailypress]

Using Google Analytics I realized a few MSN referral keywords being random numbers (i.e. 87623487235). Has anyone had the same issue or knows what that means? I did a search on those numbers and my website did not show up!

Is hacking a possibility? or is it simply an error?

[Receptional]

Maybe via MSN's new content match? There they wouldn't HAVE a keyword, but might need the audut trail.

If you are using Adcenter and having done much with it lately, then these would have been switched on by default last week.