Wheniwasyourage
Thanks, OakDryad. That's interesting and worrying! But helpful too. 
You're welcome. It's a good argument for changing passwords frequently and having a different password for each site and app that you use. That at least minimises the risks if data is shared via malware.
One of the things we overlook is the degree of cross-application click-driven data sharing. GN is doing this. For example, I browsed a book thread here, many books I had never heard of. When I went to Amazon, same day, still logged into GN, there were all the books listed in "you might like". Facebook is probably the worst for this kind of thing. Your data is never safe with FB and why Zuckerberg has been fined billions of dollars for data breaches and is now facing another trial. That is definitely one to sign out of or not use at all if you can avoid.