Spokeo

How does Spokeo know which Digg and MySpace accounts belong to a particular email address? I'm not outraged, just curious.

Update:
Digg = Add Friends > Search for Friends > Search by email (My Profile > Settings > Advanced Options > Allow others to search for me by my email address (on by default))
MySpace = Search > Find a Friend > Email (can't find a way to disable this)

Update: IdentiFight!