graeme_p - 11:47 am on Apr 14, 2011 (gmt 0)
I think its a mistake. You need to know what ads are showing on your site. I have often blocked ads I have seen when looking at the site for some other reason.
Adsense support have told me that they are not concerned about occasional accidental clicks.
..also depends which OS you run
Pretty much the same on Windows and Linux. MacOS use Netinfo which has a GUI to configure it. Mandriva Linux and its derivatives have a GUI for configuring the hosts file.