Yahoo is using “web beacons” to track you OUTSIDE of the yahoo network.
Read the “Outside the network” part of their privacy policy–there is a
link where you can opt out of this.
http://privacy.yahoo.com/privacy/us/pixels/details.html
Note that you have to opt out of this on each computer and each browser you use.
Also note that when you click on the less than obvious link, that Opt’s you out, they put a friggin’ form button on the “Successfully Opted Out” page that cancels your opt-out request!!!
I fell for it, and most users will too.