Web bugs are interesting little creatures. They are a 1 pixel graphic, easily hidden within an HTML email. If you open the message, your browser dutifully retrieves the graphic from the host server, and that action can be tracked and linked to the email sent to you.
This was used by spammers to confirm an active email account. They would blast out a million emails, and the ones that opened the ones containing web bugs would be flagged as 'known active' and subsequently further targeted for spam or for hacking attempts.
It is a universally reviled practice.
And AT&T is doing it again, probably in the name of market research.
http://www.zdziarski.com/blog/?p=1137http://tech.slashdot.org/story/10/12/03/1845212/Web-Bugs-the-New-Norm-For-BusinessesThe solution: if you receive an email from AT&T, don't open it. You can usually tell from the subject if it's marketing spam or something important. If it contains a bug, they cannot track whether or not you received the email, they can only tell if you open it. (obviously they'd know if it bounced as undeliverable) You can also program most email clients to block embedded graphics, which is also a good solution. The Outlook client lets you block and includes a button to show graphics, as does Yahoo Mail.