I found this on another Yahoo group I'm a member of.

"Yahoo has just made a sneaky change to everybody's 'Marketing
Preferences', the result of which will be a load of spam. To change
them back here's what you need to do to avoid all the ads.

"Go to My Groups and click on Account Info, verify your password if
it asks you to, and your Yahoo ID card comes up. Click on 'Edit your
Marketing Preferences' and change all those Yes's back to No's! Click
'Save Changes.'"

--mark h