Coffee chain Starbucks has said it has taken action to stop customer laptops being used to generate the cryptocurrency Monero.
On Dec 2, a Twitter user called Noah Dinkin posted a screenshot that showed that the public Wi-Fi available in a Starbucks store in Buenos Aires, Argentina, had been hacked and edited with unusual code.
Dinkin claimed the code forced a delay when he first connected to the internet there, allowing the Wi-Fi provider to mine bitcoin using his computer's processing power.
Bitcoin miners use computing power to solve mathematical problems which underpin the blockchain technology that records bitcoin transactions. Those carrying out the mining are then issued bitcoins as payment for their work.
Since the tweet, both Hackread.com and Blockexplorer.com have reported that the script was in fact Coinhive code, which was used to generate Monero coins.
According to Hackread.com, the culprit is likely not to be the Wi-Fi provider, but cybercriminals who have recently been identified as inserting the script into more than 5,000 websites.
In a response late Monday, Starbucks said the internet connection at the Buenos Aires store had now been made safe.
The coffee chain did not explain why the Wi-Fi script was able to have been changed in the first place.
This article was first published in CNBC.