Baby monitors and smart security cameras used in homes risk being hacked by cyber criminals, security chiefs warn today.

They fear weak passwords can allow online attackers to control wireless cameras and spy on families in their homes.

These cameras, and baby monitors linked to the internet, are 'vulnerable' to attack, said the National Cyber Security Centre.

In an unprecedented warning, chief executive Ciaran Martin said: 'We are bringing more of these things into the home and that brings new vulnerabilities.

On December 4 eight-year-old Alyssa LeMay was startled by a hacker's voice talking to her through a smart camera's intercom feature as she played in her bedroom in Mississippi, U.S.

'People will be concerned about privacy. If you take control of a camera, you can do whatever that camera can do. It can allow you to look around the home.

'If there are minors, they can be seen.' He added this did not mean children could be physically harmed: 'It doesn't turn into a weapon, it just means the attacker can control the camera.'

Advice to consumers to keep their devices safe includes using stronger passwords. 'This is about good housekeeping, it is not about panicking about a significant problem', added Mr Martin.

'We see sporadic evidence on cyber criminals interested in exploiting this type of vulnerability. We are not saying this is happening on a large scale.'

Smart CCTV cameras in homes use wi-fi to connect to the internet so they can be operated remotely

The rare warning follows research by consumer group Which? exposing serious security flaws in devices including wireless cameras and toys such as walkie talkies.

Smart CCTV cameras in homes use wi-fi to connect to the internet so they can be operated remotely. This means cyber criminals could hack into the cameras and look around the home if, for example, they intended to burgle the property.

In a similar way, baby monitors often offer a function for parents to monitor their child via their phones using the internet.

Dr Ian Levy, technical director of the NCSC, said: 'Smart technology such as cameras and baby monitors are fantastic innovations but without the right security measures they can be vulnerable to cyber attackers. We want people to continue using these devices safely which is why we have produced new guidance.'

Baby monitors often offer a function for parents to monitor their child via their phones using the internet

The NCSC advises consumers to take three steps, starting with changing the default password to a secure one, such as three random words.

It also recommends regularly updating security software and disabling the remote access feature if they are not using it.

New laws will ensure smart devices sold in the UK adhere to rigorous rules as part of the Government's five-year £1.9billion cyber security strategy.

Companies will have to supply unique passwords, give shoppers a contact for concerns and issue guidance on security updates.