-I haven't signed into that Yahoo account for 2 weeks. Haven't spoken with that person for ~4+ months. -I've never let Facebook search my Yahoo contacts or vice versa.
-My usernames are different.
-My Yahoo account name & the name I gave in chat is different from my Facebook name.
-I've made searches for contacts on my Yahoo in the Facebook search eg `[email protected]`.-I don't have a phone number stored in Yahoo or Facebook but I've typed one into both in chats or messages.
-I don't have any photos on Yahoo that match my Facebook photos, but I have sent photos through Yahoo that match one of my Facebook photos.
-Their recent activity: ` NAME changed profile picture. NAME is now friends with FOOBAR and 6 other people.`
Cookie sharing? Treachery? What could I have missed that would let this happen?