BT's Home Hub system is open to hack attacks, security experts are claiming.
Security specialists say that millions of BT customers could be at risk because hackers need only download software, which can be found on the Internet, to then crack passwords and change settings on the Home Hub system in as little as 5 seconds.
BT is aware of the problem but says that the risks are merely "theoretical" and that hackers would have to "win the computer cracking equivalent of the National Lottery" to succeed.
But Paul Vlissidis, technical director of IT consultancy NCC Group, told The Telegraph that the telecoms company is underestimating the problem.
"All the bad guys know about this", he warned. "It is very widely published on the internet and the software is very easy to get hold of. The only people that don't seem to be aware are the customers of the networks."
BT is advising customers to check www.bt.com/help/hub for advice.
"All wi-fi networks could be vulnerable to a determined hacker intent on breaking the law, and of course people have to take care", a BT spokesman said.
"We entirely reject the idea that our customers' bank or credit card detail are at risk. That's complete nonsense."