The free Wi-Fi that the Buenos Aires Starbucks offers to its customers was being used to mine for cryptocurrency, and what’s worse, it used people’s laptops to do it.

The whole thing was discovered by Stensul CEO Noah Dinkin who actually paid a visit to the store and wanted to browse the web using the free Wi-Fi, only to discover that his laptop was unknowingly converted into a cryptocurrency miner.

He then turned to Twitter to ask Starbucks if they know about the what he described as bitcoin mining taking place without customers knowing about it.

“Hi Starbucks, 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,” he said in his tweet.

Even though Dinkin says the Wi-Fi was used to mine for Bitcoin, it turns out that the cryptocurrency in question was Monero, a less known alternative whose main focus is privacy.

Starbucks blames the Wi-Fi provider

Starbucks only answered on December 12 to explain that everything happened without the store knowing about it, suggesting that it was the fault of its Wi-Fi provider.

“As soon as we were alerted of the situation in this specific store last week, we took swift action to ensure our internet provider resolved the issue and made the changes needed in order to ensure our customers could use Wi-Fi in our store safely,” the firm said in a statement.

In a more detailed response for Motherboard, Starbucks spokesperson Reggie Borges explained this was just an isolated case, and it’s not happening in all stores.

“Last week, we were alerted to the issue and we reached out to our internet service provider—the Wi-Fi is not run by Starbucks, it's not something we own or control. 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,” he said.