Players whose accounts are inactive and want to try out the newest patch in order to get ready for Mists of Pandaria, can claim their free seven days of game time. This offer is limited and must be claimed before September, 19th.
It's recommended to directly log in to Battle.net to avoid any possible scams.
Most scammers will probably try to scam the account off you so be cautious.
If you haven't received an official email yet, try to visit this link.
My inactive account from August, 28th was not eligible to claim this offer, so you'll probably need to have an account frozen for at least a month.