Rovio has recently updated the original Angry Birds apps for iPhone and iPad in celebration of Angry Birds’ second birthday (which is today, December 11), adding 15 new levels and unlocking every episode within both applications for users to play through.

As outlined in the apps’ release notes:

HAPPY BIRDDAY!

The Angry Birds are celebrating their 2nd birthday, but the pigs are crashing the party and it’s up to you to save it!

As a birthday gift to our fans, all episodes are now unlocked!

Satisfy your sweet tooth with 15 brand new birthday cake levels!
Celebrate 300 LEVELS of Angry Birds!

Party with the amazing expandable orange bird!
Check out the spiffy new menus and graphics!
Special birthday achievements make this update a treat!

Since its release in the App Store, Angry Birds has proved to be an incredibly successful iOS game, spawning a number of sequels and merchandise (there’s even talk of movie and TV adaptations, too!).

Now, Rovio is celebrating Angry Birds’ second birthday in style, and it’s great to see fans of the app rewarded in “version 2.0″ of both Angry Birds for iPhone, and Angry Birds HD for iPad.

If you haven’t yet purchased either app, you can grab Angry Birds for $0.99 and Angry Birds HD for $4.99. However, if you already own both Angry Birds applications, the updates are free to download.

Check out the celebratory Angry Birds updates now, and be sure to post your thoughts in the comments.

[via Mashable]