HACKERS could hold people to ransom through personal data obtained from their smartphones, watches, television and even fitness trackers, cyber security experts have warned.

The National Crime Agency (NCA) and National Cyber Security Centre (NCSC) said in a report that ransomware – which renders devices unusable until their owners pay to have them unlocked – has become increasingly prevalent over the past year.

Their joined report, presented to the CyberUK conference in Liverpool, said cybercrime is becoming more aggressive and the risk to business was “significant and growing”.

They warned that devices holding photos, emails and fitness information could be targeted, and increasing numbers of gadgets connecting to the internet meant greater opportunities for criminals.

The report said any devices containing personal data, such as pictures, which people considered valuable enough to pay for, could be targets.

“This data may not be inherently valuable, and might not be sold on criminal forums but the device and data will be sufficiently valuable to the victim that they will be willing to pay for it,” said the agencies.

“Ransomware on connected watches, fitness trackers and TVs will present a challenge to manufacturers, and it is not yet known whether customer support will extend to assisting with unlocking devices and providing advice on whether to pay a ransom.”

Their report also outlined how the most sophisticated criminal gangs were able to use the same high-tech tools as states to target financial institutions.

Others were able to carry out attacks using more basic software on smaller business and the general public.

With as many as 21 billion devices used by businesses and consumers forecast to be connected to the internet worldwide by 2020, cyberattacks will continue to evolve and security agencies and companies are pulling out all the stops to cope with them.

The increasing popularity of the Internet of things (IoT), which sees smart TVs, laptops and other connected devices that turn houses into “smart homes”, has triggered rising demand for home “firewalls”, designed to secure all your gadgets.

They have names such as RATtrap, from IoT Defence, F-Secure’s SENSE and Cujo, and retail from £100 upwards, but all have the same purpose.

Cujo – which takes its name from the rabid dog that featured in Stephen King’s novel of the same name – promises to CUJO secure everything from smartphones and laptops, to TVs and baby monitors.

The multi award-winning company says antivirus programs alone can’t protect people from hackers.

“You can install it on your laptop, but not on your iPhone, smart thermostat, and Wi-Fi camera,” it says.

“Traditional security solutions are outdated with cybercriminals creating new ways to reach into our homes every day.

“CUJO uses threat intelligence, machine learning, and cloud-computing to analyse your device behaviour.

“When we see a threat – we block it. You will get a friendly notification on your CUJO app that your home is safe.

“We guard every single connected device including baby monitor, thermostat, TVs, lights on your network, not just a PC.”

Cujo plugs into a home network through a network cable and will automatically break down local and internet traffic.

It then sends statistics on that data to the cloud for further analysis and if suspicious activity is detected, it will block it and let you know via a mobile app.

It also includes a parental control feature to allow parents to monitor and control their children’s online activities from a phone, computer or even a game console.