I had a similar problem. Something sent emails with a mysterious link to essentially everyone on my Yahoo contact list. Up to that point, I didn't have anyone in my Yahoo contact list! I intentionally didn't add anyone becasue I didn't want this to happen.

Apparently, my Yahoo contact list on my laptop was created/updated by wireless sync from my Blackberry. Before I understood where these contacts came from, I deleted all my Yahoo contacts (on my laptop) and, you probably know where this is going, next time I went to send something from my phone, my contacts were wiped.

I have since disabled the sync feature for the Yahoo email address (click on the email account - options - email reconcilliation - uncheck Wireless Reconcile). For my purposes, it certainly caused more problems than it was worth.