Happy Birthday, Angry Birds!

Releasing one of the most popular mobile games of all time exactly two years ago today, Angry Birds developer Rovio celebrated Sunday by adding 15 new levels and unlocking older ones on iOS, according to reports.

As a birthday gift to our fans, all episodes are now unlocked, Rovio said in an update on the iPhone's app store. Satisfy your sweet tooth with 15 brand new birthday cake levels! Celebrate 300 levels of Angry Birds.

New menus and graphics were also released. Kotaku reported that the new 15 levels will have players flinging the birds into cakes, balloons and other festive objects, including a new projectile, the Orange Bird, which propels any object it touches.

According to Mashable, Rovio also teamed up with Barnes & Noble on Sunday from 11 a.m. to 3 p.m. to host various special events such as scavenger hunts, high-score contests, Angry Birds character designing, parades and guessing games in numerous U.S. Barnes & Noble stores.

Joystiq.com reported that Toys R Us offered a 25 percent discount on Angry Birds plush toys, including an unlock code for an Angry Birds Chrome Seasons Greedings bonus level.

Mashable reported that Rovio's CMO says Angry Birds is now worth more than $1 billion. As of last month, fans have played 266 billion levels, shot 400 billion birds and collected 44 billion stars. The company also said that people play Angry Birds for a combined 1.825 billion hours per month.