Twitter, on a support page for their “app graph”:

To help build a more personal Twitter experience for you, we are collecting and occasionally updating the list of apps installed on your mobile device so we can deliver tailored content that you might be interested in. If you’re not interested in a tailored experience you can adjust your preferences at any time (read below). Additionally, if you have previously opted out of interest-based ads by turning on “Limit Ad Tracking” on your iOS device or by adjusting your Android device settings to “Opt out of interest-based ads,” we will not collect your apps unless you adjust your device settings.

This only applies to Twitter’s first party clients but still, it’s pretty worrisome and a blatant invasion of their users' privacy. Even if most users were interested in having “tailored content” delivered to them, this is something that clearly should be opt-in.

Via Chris Gonzales.