Pen Test Partners showed the BBC how it could gain access to a Hero4 camera that appeared to be turned off, to secretly watch or eavesdrop on users, or to view and delete existing videos.

The attack relied on victims setting simple passwords which could be guessed by software within seconds.

GoPro said its security was adequate.

Taking control

Ken Munro, a partner at Pen Test Partners, also said the way the cameras were set up meant that a wireless connection can unknowingly be left on after the power button on the device had been pressed to turn it off.

He showed how he could "wake" the device, turn off its recording lights, and then video-stream what the device could see to his own mobile phone.

Mr Munro said that in order to take control, a criminal would need to intercept and crack the encrypted Wi-fi key, which is set up by the user when they connect the camera to a mobile device such as a phone.

In his demo he captured the key using a laptop and some free specialist software.

'Sausages'

To make his point, Mr Munro then showed the BBC how his firm was able to use software freely available on the internet to guess the password a user might have set.

In this case the word "Sausages" was used as the password and the software guessed it in less than one minute.

The software tries thousands of possible passwords each second, using a dictionary of those known to be most commonly used.

Mr Munro wants GoPro to actively encourage users to set stronger passwords.

"Cybercriminals are increasingly turning to cracking passwords to gain access to accounts" he warned.

GoPro response

"We follow the industry-standard security protocol called WPA2-PSK (pre-shared key) mode," GoPro told the BBC, in a statement responding to details of the demonstration.

"Wi-fi-enabled devices must provide the user's password to access the Hero4 wi-fi network. This is the same as other wi-fi networks using that protocol," the firm said.

"We require our customers to create a password 8-16 characters in length; it's their choice to decide how complex they want it to be.

"As is true of all password-protected devices and services, if a password is easily guessable, a user is more prone to someone predicting what it is," GoPro added.