Yahoo is now using something called "Web Beacons" to track Yahoo Group users around the net and see what you're doing - similar to cookies. Take a look at their updated privacy statement
About half-way down the page, in the section "Outside the Yahoo! Network", you'll see a little "click here" link that will let you opt-out of their new method of snooping. You may want to do this. Once you have clicked that link, you are opted out.
Notice the "Success" message at the top of the next page. Be careful, because on that page there is a "Cancel Opt-out" button that, if clicked, will *undo* the opt-out.
Sneaky little devils!
I strongly suggest that if this applies to you, you opt-out. Where you go and what you do online is your business, not Yahoo's.