An electronic census of the internet's 2.8 billion addresses has been completed by US researchers. It is the first attempt to contact every web address since 1982 – the results could help tackle the problem of the supply of unique internet addresses running out.
John Heidemann and colleague Yuri Pradkin at the University of Southern California, US, sent probes – known as pings – to each of the billions of unique IP addresses that make up the internet over a period of 62 days.
IP addresses uniquely identify network devices on the internet. Some map to human-friendly web addresses such as www.newscientist.com.
Due to security settings on some servers, about 61% of the pings received no response at all, and others received responses equivalent to "no comment". Millions of servers did respond, though, allowing Heidemann and Pradkin to build an 'atlas of the internet' (see right, top).