Cyberclinic: How do these websites know where I live?

Graham Perkins emailed, complaining that the internet radio service Pandora.com was unavailable to UK users. We're not the first country to lose access to its customised music stations – most Western European listeners were shut out a few months back, and now Pandora has become a US-only service while arguments over licensing and copyright rumble on. Other sites, such as last.fm, will scoop up Pandora's listeners – but how does a website know which country you're in? And why did Pandora's statement say, "users in the UK and elsewhere will still be able to utilise the service through other means".

It's relatively easy for a site to spurn you if it knows your internet address, or "IP". Filesharing sites have shut out employees working for copyright organisations after obtaining their IP details. But how do those IPs – seemingly random sequences of numbers – relate to a countries?

Blocks of IPs are assigned by the Internet Assigned Numbers Authority to global bodies that allocate blocks to countries and organisations – so your location will usually be betrayed by your IP. If you want to see where the web thinks you are, visit www.tinyurl.com/y4787p. As the software needed for a site to obtain these details is free, it's simple to block visitors from New Zealand or Norfolk. In theory, you can use a proxy server to fool a website into thinking you're somewhere else. Many websites provide lists of proxies, and with Firefox you can go to your network settings page, type in the proxy address and your net surfing will be cloaked in secrecy.

However, proxy servers don't always work well. I spent half an hour going through one list in an attempt to connect to Pandora, but without success; then I discovered that someone has already set up a website – globalpandora.com – that uses proxies to connect to the service. It's experiencing "unexpected technical difficulties". Proxies can make IP blocking ineffective, but when thousands of people are overloading proxies to beat the blocks, only a handful of people will get through, causing little bother to the site concerned.

Diagnosis required

What are these "del.icio.us" and "digg" buttons after blog posts? Can information about me on the web be erased? Email cyberclinic@independent.co.uk, or join the discussions on the daily technology blog, independent.co.uk/cyberclinic