Connected or 'smart' toys are going to be top sellers this Christmas - but parents are being warned about "vulnerabilities" that could be child safety risk.

Consumer group Which? has tested four toys - the Furby Connect, i-Que Intelligent Robot, Toy-Fi Teddy and Cloud Pets - and found these could be used by a stranger to talk to your child.

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The testing found the Bluetooth connection in each of the toys had not been secured, meaning a hacker would not need a password or PIN code to achieve access.

In addition, "very little technical know-how" was needed to gain access to the toys to start sharing messages with a child, the watchdog said.

The results found anyone within a 10 to 30-metre Bluetooth range of the Furby could connect to the toy when it was switched on.

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The investigation shows anyone can download the app for the i-Que Intelligent Robot and start chatting using the robot’s voice by typing in the text field.

The Toy-Fi Teddy lacked any authentication protections, meaning the watchdog's hackers could send their voice messages to a child and receive answers back.

And the Cloud Pets toy could be hacked via its unsecured Bluetooth connection and made to play voice messages.

Alex Neill, Which? managing director of home products and services, said: “Safety and security should be the absolute priority with any toy. If that can't be guaranteed, then the products should not be sold.

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"Connected toys are becoming increasingly popular but, as our investigation shows, anyone considering buying one should apply a level of caution."

Vivid Imaginations, which distributes the i-Que robot toy, told Which? the toys fully comply with the Toy Safety Directive and European standards.

Hasbro, which makes the Furby Connect, said: "We feel confident in the way we have designed both the toy and the app to deliver a secure play experience."

Spiral Toys declined to comment to Which? in relation to Cloud Pets and the Toy-Fi Teddy.