My Permalinks changed, hacked?

I went to visit my site tonight and got a “Bad Request” error attempting to access ANY page from the homepage.

Upon further inspection I found that there was a VERY weird permalink structure in every link. It was something like:

/2009/09/03/{__eval(‘appchatter.com’)__}/post-tile-here/

it wasn’t exactly like that, I didn’t bother grabbing the link structure. However, I immediately went in and checked the permalink setting and it had changed. So I just simply clicked it back to the “/month/title/” setting that I’ve always used. However, prior to changing it back it was set to a custom permalink that was NOT even close to being what I had setup.

Luckily the site was only down for about an hour before I noticed it, but this one is REALLY odd. None of us have logged into the site since early this morning and our visit count is only down during the hour prior to the link change discovery.

I’m wondering if this is a known security vulnerability?? Can this be changed by someone crafting a URL and just hitting the site? or …?

I’m running 2.7.1.