Hacker News Reader

Mostly to scan the PDF and ensure it's safe I believe, or atleast that's would be the stated reason.

I can believe that (despite the obvious creepyness), since FB users have a knack for getting owned and spreading that ownage to other users.

PDF is an open format. Scanning PDF for the links is probably the least you could assume.

You gotta assume they will reconstruct generations of your family tree if they can from your chat history.

"...reconstruct generations of your family tree if they can from your chat history."

People might pay good money for that!

Then people have strange assumptions.

Once a service starts blocking malicious links, the obvious next step is to conceal the link through some sort of indirection.