A tweaked version of the Firefox browser that makes web browsing anonymous has been released by a group of privacy-minded coders.

Every few minutes, the currently Windows-only Torpark browser causes a computer's IP (Internet Protocol) address to appear to change. IP addresses are numeric identifier given to computers on the internet. The number can be used along with other data to potentially track down a user, as many websites keep track of IP addresses.

Torpark's creators, a group of computer security gurus and privacy experts named Hactivismo, said they want to expand privacy rights on the internet as new technologies increasingly collect online data.

The browser is free to download. It's a modified version of Portable Firefox, an optimised version of the browser that can be run off a USB (Universal Serial Bus) memory stick on a computer.

The Torpark browser uses encryption to send data over The Onion Router, a worldwide network of servers nicknamed "Tor" set up to transfer data to one another in a random, obscure fashion.

Internet traffic, such as site requests, carries information on where it came from and where it's going. But that's muddled using Tor, which has been endorsed by the Electronic Frontier Foundation, and is hard to trace back to a source.

One minor downside is that surfing with Torpark is slower than with a typical browser over the same connection.

Torpark cautions that data sent from the last Tor server to the website is encrypted. Since only the user's connection is anonymous, Torpark advises that sensitive data such as username and passwords should only be used when the browser displays a golden padlock, a sign that a website is using encryption.

Torpark's user interface appears similar to Firefox with a few changes. It shows the current IP address that would be seen by websites in the lower right-hand corner, and features a special 'Flush Tor' button to reset a new, random server connection.

A test of Torpark using a computer in London employed IP addresses of servers registered in Berlin and Madison, Wisconsin.