"(We collect) hardware model, operating system information, battery level, signal strength, app version, browser information, and mobile network, connection information including phone number, mobile operator or ISP, language and time zone, and IP, device operations information, and identifiers like device identifiers (including identifiers unique to Facebook Company Products associated with the same device or account)

"...how you interact with others using our Services, and the time, frequency, and duration of your activities and interactions), log files, and diagnostic, crash, website, and performance logs and reports. This also includes information about when you registered to use our Services, the features you use like our messaging, calling, Status, or groups features, profile photo, about information, whether you are online, when you last used our Services (your "last seen"), and when you last updated your about information.

"We collect device location information if you use our location features, like when you choose to share your location with your contacts, view locations nearby or those others have shared with you, and the like, and for diagnostics and troubleshooting purposes such as if you are having trouble with our app's location features. We use various technologies to determine location, including IP, GPS, Bluetooth signals, and information about nearby Wi-Fi access points, beacons, and cell towers.

"We receive information about you from other users and businesses. For example, when other users or businesses you know use our Services, they may provide your phone number, name, and other information

"Businesses you interact with using WhatsApp provide us information about their interactions with you.

This reminds me Windows 10 collecting color of the device, in that it is unnecessary for operation but enough to pinpoint a person in combination.

Unless the open source app is transparently built and app store deployed from a public build server, it's very easy for the owner to inject a back-door into it.

There's no mechanism built into the app stores to validate an app against its source code.

So the owner could checkout master, add a back-door, build and publish to the app stores, and you'd update, never knowing you're exposed.

Nothing is 100% safe. It's just dependent on how much trust you assign.

These applications are super complex and you can't count on all eyeballs detecting a potential backdoor. And, you don't know if the code in the repo matches what you download from the App Store.

You are also right that appstores are a problem. However, one of the nice things they do is using signatures to prevent tampering with the builds. So having a build system that produces reproducible builds and signatures means users can check whether things line up.

A bigger problem is the reliance on the phone network for identity. A lot of these chat clients insist on using telephone numbers for identifying users. This has been used to shut down chat networks in countries with telecom operators that are collaborating with governments.

If you want to stay secure, most of the chat apps out there are problematic at some level. Signal is one of the very few decent options out there. It is one of the few solutions that has both open source clients and servers and a wide community of people using it and scrutinizing it. With e.g. whatsapp, you are at the mercy of a multinational with a track record of indifference and negligence towards the goal of preserving their user's privacy and, worse, a strong incentive towards doing the exact opposite.

As for not knowing what has been downloading (if someone tempered with), the best approach is compiling it on your own.

The reason I ask is that this is an oft repeated claim about open source by developers yet when I talk to security people they don’t seem to care about open source nearly as much. To them inspecting binaries is table stakes anyway.

Meanwhile people write backdoors that aren’t obvious for fun. http://underhanded-c.org/

Eventually, maybe. How many eyeballs and how long to find Heartbleed?

Bringing this up as an argument is a sensible as claiming that transparency and democracy isn't any better than a dictatorship because there is still corruption.