Jane wrote in the tweet:
Facebook will scan the user's system library in the background through their Android app and upload it to one of their servers. This is called the Global Library Collector. It is referred to as GLC in the application code. It periodically uploads the metadata of the system library to the server.
Facebook's GLC doesn't have an exit option, and it's impossible to see what's collected from our device. It's not clear what GLC is, but I think it should be designed to ensure system integrity and compatibility.
To make matters worse, the Facebook app knows to compress each file before uploading, which makes sense if you want to minimize traffic. But it seems that the file will also go to a user-specific collection.
It's unclear what the purpose of this data collection is, how Facebook handles the data, and whether the user agreement covers uploads. It is probably a security measure, but unless the company really solves the problem, it is still in a very dark area.