Optic Nerve was one of these things. Basically, GCHQ or NSA hacked Yahoo!, GCHQ used that to collect stills for every single webcam feed on the platform (this! was! back! when! Yahoo! was! still! relevant!), including a lot of intimate photos, so on. Lots of fun stuff there!

But that's a modern example. There are some pretty interesting ones. Here's a fun list of some celebrities that were the targets of a Five Eyes country and were spied on by multiple agencies as a result:

https://en.wikipedia.org/wiki/List_of_people_under_Five_Eyes...