I've been seeing this in pop-up ads, too. The word "broadcast" is kind of misleading. Imagine that... a pop-up ad that's misleading. Who woulda thunk? ; )
Anyway, you aren't really broadcasting your IP address. It's not like anyone anywhere on the Internet could just listen in to your broadcasted signal. That's what a broadcast would do, and the Internet doesn't work that way.
However, there is a small grain of truth there. When you surf the Web, anyone on a LAN between your browser and the Web server can see your IP address and where you are surfing. That means, anyone on your LAN, anyone at your ISP on the path of the packets, anyone at any other downstream ISP where the packets travel, and anyone at the Web site you are surfing to can look at your IP address and your surfing habits. So, while it's not broadcasting, the potential is there for some people to look at your address.
What can you do to stop this? First off, don't click on any annoying pop-up ad offering a solution. If you are surfing to sites and really need your anonymity and privacy, you may consider using a service like Anonymizer. Surf to www.anonymizer.com. There, you can access all other Web sites. Everything identifying you, including your IP address, is stripped off at Anonymizer. They have a free service, which is very slow. Alternatively, they have a pay service that is much quicker.
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This was first published in February 2003