A weakness that left thousands of Virgin Media routers vulnerable to attack also affects devices by other providers, security experts suggest.
Virgin Media’s Super Hub 2 was criticised for using short default passwords that could easily be cracked by attackers.
But experts raised concerns that older routers provided by BT, Sky, TalkTalk and others were also at risk.
They recommend users change their router password from the default.
“It’s a bit unfair that Virgin Media has been singled out here. They made a mistake – but so have many other internet service providers,” said Ken Munro from security firm Pen Test Partners.
“This problem has been known about for years, yet still ISPs [internet service providers] issue routers with weak passwords and consumers don’t know that they should change them.”
The weakness in Virgin Media’s Super Hub 2 was highlighted in an investigation by consumer group Which?
The company has since advised customers using default network and router passwords to update them immediately.
However, a BT spokeswoman told the BBC: “We are not impacted by the hub issues affecting Virgin Media.”
Other providers have yet to comment.
What makes a router vulnerable?
Many routers are sent to customers with a default wi-fi password already set up.
Some use a long password with mixture of upper and lower-case letters, numbers and sometimes symbols.
But others use short passwords with a limited selection of characters, and many follow a pattern than can be identified by attackers.
The Virgin Media Super Hub 2 used passwords that were just eight characters long, and used only lower-case letters.
That gives cyber-criminals a framework to help them crack passwords quickly, using a dedicated computer.
“Because the default wi-fi password formats are known, it’s not difficult to crack them,” said Mr Munro.
Once an attacker has access to your wi-fi network, they can seek out further vulnerabilities.
Mr Munro said the problem was well-known, but the Which? investigation had reignited discussion.
“It has popped up again because attention has been drawn to the fact that very few people change their wi-fi password from the one written on the router,” he told the BBC.
Experts recommend that people change the default wi-fi password and router’s admin password, using long and complex passwords to make life more difficult for attackers.