Monday could mean lights-out for millions of internet users

Thousands of computers in more than 100 countries could lose internet access on Monday as a result of the FBI shutting down servers previously used to host malicious computer software.

The software, known as DNS Changer, controlled which web pages people saw without their knowledge. This was done by changing the Domain Name System (DNS) settings on a computer to point towards malicious websites. In November last year an FBI investigation into the attacks led to six arrests in Estonia.

The threat surfaced in 2007 and the FBI says it could have infected more than 500,000 computers in the US alone. The criminals used DNS Changer to manipulate internet advertising, netting them £14m in revenue. In its investigation the FBI found that in some cases system updates and anti-virus software stopped working, exposing infected computers to more threats.

When the arrests took place, the FBI took control of the rogue DNS servers and removed the malicious software. The servers were left running in order to give users of infected computers time to remove the DNS Changer by changing DNS settings.

Time is now running out for people to check and change their DNS settings if necessary. The FBI is switching off the servers on Monday 9 July. Anyone who has not changed their DNS settings could lose their internet access.

To check if your system has been infected, go to the DNS checking tool at http://www.dns-ok.us.

The FBI has also produced an in-depth guide to checking and changing DNS settings.