As part of Atari’s 40th birthday, the publisher just announced an interesting promotion that lets you grab all of its classic game ports for the iPhone and iPad totally free of charge.

The Atari’s Greatest Hits app has always been a free download, but each of a hundred Atari 2600 and arcade games found in this collection is normally a paid download through in-app purchases (except Missile Command).

You don’t want to pass on this one, but there are some caveats you should know about…

Atari tweeted an hour ago:

Atari’s Greatest Hits promo for iOS is extended! 100 classic titles in your pocket for FREE, now until 11:59pm EST 6/28.

Upon launching the app, a dialogue box informs you that all games will remain free to play until you remove or reinstall the game. Normally, you can either buy 25 separate packs in-app for 99 cents or get all hundred titles for ten bucks.

So if you want to take advantage of this promotion, you’re advised to download and install the app on all your iOS devices and then on each device download whatever game you want to play for free and keep.

The app has amassed over five million downloads since its release last April.

Are you a sucker for classic Atari hits?