Over the past year, Bitcoin has seen its value increase by 1,000 per cent, so its perhaps unsurprising that its become an attractive target for hackers.
In a process called cryptojacking, cyber criminals are taking over networks and computers to put them to use in mining the cryptocurrency and others like it.
Among recent high profile targets was a public Wi-fi at a Starbucks, where suspicious code was found that turned visitors’ devices into money makers for crooks.
Noah Dinkin, chief executive of email provider Stensul, raised the alarm after visiting one of the coffee shop’s franchises in Buenos Aires.
He discovered that anyone who connected to the store’s hotspot was at risk of having their gadgets put to work mining Monero, another digital currency.
Writing on Twitter, he said: ‘Hi @Starbucks @StarbucksAr did you know that your in-store wifi provider in Buenos Aires forces a 10-second delay when you first connect to the wifi so it can mine bitcoin using a customer’s laptop?
‘Feels a little off-brand.’
Starbucks was quick to respond and took action with a third party Wi-fi supplier to remove the malicious code.
A spokesman said: ‘We want to ensure that our customers are able to search the internet over Wi-Fi securely, so we will always work closely with our service provider when something like this comes up.
‘We don’t have any concern that this is widespread across any of our stores.’
Cyber-security experts say they have seen a spike in cryptojacking, which can slow down your computer, in recent months.
Cryptojacking is defined as the secret use of your computing device to mine cryptocurrency.
It used to only happen when a victim unknowingly installed a malware program designed for the task.
That means the malicious code responsible for in-browser mining loads whenever the web page is accessed.
If the mining is being limited to stay below a certain threshold, you may not even notice it’s happening.
But if the mining is not being throttled, you will likely notice some impact on performance.
Many users who have been hit notice slower speeds, usually caused by a drain on their CPU.
You may also notice cooling fans on laptops and desktops whirring up to high speed to compensate for the jump in activity.
Starbucks is by no means the only firm to be affected by the issue, with numerous companies and home users believed to be infected.
In September, cryptocurrency miners were found running on websites owned by Showtime, the Pirate Bay, Politifact and the UFC.
In recent days it emerged that video streaming sites like Openload, Streamango, Rapidvideo and OnlineVideoConverter have also been affected, according to security firm Adguard.
Almost one billion visitors to the four popular video sites each month are being unknowingly mining cryptocurrency, the firm says.
The mining program loads in a user’s browser when the video player is downloaded ready to stream the video.
In a blog post, Andrey Meshkov, co-founder of the company, said: ‘We came across several very popular websites that secretly use the resources of users’ devices for cryptocurrency mining.’
‘The total monthly earnings from [this] cryptojacking, taking into account the current Monero rate, can reach $326,000 (£240,000).
‘These are simply outrageous figures.’