Twitter, hungry for new data to fuel its targeted advertising, will start looking at what other apps its users have downloaded.

Starting Wednesday, the company will begin collecting data on which other apps its users have on their iOS and Android smartphones. The data, Twitter says, will help it deliver better “tailored content” to its users. That’s sure to include ads, but maybe also better recommendations about whom to follow when users sign up, or more relevant first tweets in the feed, which could help Twitter hook people early.

It’s strictly a list of the apps users have installed, Twitter says, not data pertaining to what people do inside those apps. So Twitter would know if you have a ride-hailing app, but it wouldn’t see your rides taken with the app.

Twitter is not the only company to collect this sort of data—other major Internet companies like Google and Facebook do it too under certain circumstances. Facebook, if a developer has integrated its software kit, might use the data for mobile app ads.

Still, Twitter’s move stands to raise privacy concerns at least among some people, perhaps depending on which other apps are on their phones.

Twitter’s data collection will start automatically, unless users have already turned on the built in “limit ad tracking” or “opt out of interest-based ads” option on iOS or Android phones, respectively. Twitter users will be notified of the data collection, but they can turn it off at any time from within their app’s settings, Twitter says. If users turn it off, the data is removed from Twitter’s servers, the company says.

Twitter currently relies on several other types of data to target ads. This data include whom individual users follow on Twitter, the composition of their social network, how they tweet, and how they interact with other tweets. Ads might also be targeted using a person’s profile information, their location, or IP address.

Adding people’s downloaded apps to the mix could help Twitter add more smarts to its ad targeting. Or not. Twitter, again, won’t be tracking how people use the apps. So if someone has a bunch of apps sitting on their phone that they rarely use, it might not help Twitter all that much just to know that they’re there.

News of Twitter’s new app collection data was first reported by Re/code.