For all you World of Warcraft or Starcraft II basement dwellers who've been yearning for an "official" Battle.net Authenticator, good news as you can go and grab it now:
"Protect your Battle.net account with Blizzard's official Battle.net Mobile Authenticator app for your Windows Phone 7 device. The Battle.net Mobile Authenticator is an optional tool that offers an additional layer of security to help prevent unauthorized account access. Each time you log in to a Battle.net account, you’ll use the Battle.net Mobile Authenticator to generate a unique, one-time use password to use in addition to your regular password. Log in with both and you can rest easy knowing that the account is more secure against unauthorized access."
Rumor has it it's as good if not better than the iPhone/Android versions. There are two other third party authenticators in the Marketplace, one from Velocity Studios ($0.99) and Robert Garfoot (free). Since we don't use Blizzard for, well, anything, we'll leave it to you to discern the finer points. Version 1.0 came out three days ago and version 1.1 just went live today, so support seems to be pretty solid.