For the past six months, Twitter has been collecting data on which smartphone apps its users download. Now, the company is using that data to make some money.

Twitter announced on Wednesday that its advertisers can use that app information to target users with ads. Marketers will be able to target you based on the different categories of apps you have downloaded onto your phone as well as how recently you downloaded them.

Twitter first announced in November that it was collecting this data, but until now, it wasn’t using it for anything. It’s easy to understand the draw from Twitter’s perspective: If Twitter knows you like Candy Crush, it may assume you like other similar games as well.

It’s also easy to understand why this type of targeting may freak some users out. You can block Twitter from collecting this data in settings, but the feature is opt-out, which means the company will gather this information unless you tell it to stop. Twitter won’t, however, have access to information within the apps you download. For example, the company may know you’ve downloaded WhatsApp, but it won’t have access to your messages.

Twitter, like Facebook, relies heavily on targeted ads for the majority of its revenue. It already targets users based on the people they follow or the things they tweet. Taking a peek at your app graph is yet another step toward understanding what kinds of things you like.