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Simply by using your IP address and a few WHOIS and DNS lookups, it's relatively easy to discover information such as your geographical location, and which ISP and DNS servers you use. In a similar fashion, every web browser carries with it a unique signature (unless you have manually changed it, which very few people do) that tells the website you're visiting which client is running and allows it to provide data tailored to suit. Visit http://whatismyipaddress.com if you want to discover just what's revealed by your browser.

Tony Fogerty is an ethical hacker with

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risk consultancy DNV IT Global Services and warns that an attacker can use this to serve up malicious web pages carrying a browser-specific exploit. "However, if you were being canny you could change your IE 'signature' to that of a Firefox browser," Fogerty advises. Use the User Agent Switcher extension at www.pcpro.co.uk/links/164hack1 to quickly change user agent strings in Firefox to Internet Explorer, Netscape or Opera. Internet Explorer users can do likewise by downloading Internet Explorer 7 Pro (www.ie7pro.com).

If you want to cover your tracks then an anonymous proxy will hide your real IP address, but this comes at a cost: financial as far as the reliable commercial proxy services are concerned, but also in terms of browsing speed and the fact that some services will block anonymous proxy users.

2. Test your firewall

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