One of my sites vanished in adsense stats, I thought maybe I lost rankings, still the same...
Checked the html source and the pub ID is not mine, checked the source on the ftp and its mine? WHF is going on? I have several sites on this shared host and this is the only site effected. I don't see any strange files in the directory.
I would definitely report it to Google ASAP and perhaps leave it as-is until they can take a look. I would even ask if they can restore your stolen income from those pages, they probably won't, but it never hurts to ask.
You may want to ask your web host to scan the server to see if this pub ID exists in other accounts as it's possible the server has been hacked, hard to know.
It's possible if the source you see on the server is yours via FTP that someone has installed a simple script and is doing a search/replace on the publisher ID before the page is sent, check your .htaccess files and see if anything new is there.
It is very unlikely that a hacker would put his own pub ID as he will not be able to cash on illegal activities via Google, most probably that other pub ID belongs to someone else the hacker is trying to get into trouble.
Good point about checking the htaccess Bill, never would have thought of it.