We have received two separate reports of Symantec AV being triggered when accessing Yahoo! Mail beta today (w32.feebs).  Apparently the issue disappeared later during the day.

If you have any further information we would be glad to hear from you!

Thanks to Agris and William for bringing the matter to our attention.

Update (again):   Multiple users wrote in confirming the observation. Symantec has stated in email that this is a false positive and they are working on a signature update to fix the problem.  There is, at present, no posting on their website with this info, though.  We'll update the story when they post something and/or when the new signatures come out.