Google just posted up on their Adsense blog that there is a new feature called site authentication.
The gist of it is that this feature will allow you to set up a user name and password for the Adsense robot.
It can then go in and crawl your password protected pages (much like a registered user) and thus begin showing relevant ads.
This overcomes a major hurdle for many webmasters. Those operating forums can breathe easy now as they can keep their spaces locked down (for whatever reason they choose to do so) and still be assured that relevant ads are being shown to users.
In fact, many sites may see an increase in CTRs as a result of a captive audience now seeing very targeted ads.
This move is a positive one as it shows Google is listening to the needs expressed by Webmasters and doing something to help them achieve their revenue goals. In the larger picture, it also acknowledges the extent to which password protected spaces have grown. Google wouldn’t be doing this if it wasn’t in THEIR best interest as well. They now have expanded their advertising exposure reach into all those previously dark nooks and crannies folks have locked down.
So, if you’re a Webmaster with anything questionable behind the locked door, better do some cleaning before setting this feature up. No worries, though, because if you don’t expressly set it up and activate it, the spiders stay out as usual… 
Good move Google.
