Researchers at Fidus Infosecurity said in a blog post that they had noticed OnePlus users discussing attempts at credit card fraud. These users said they had used the cards in question only on the OnePlus website in November last year.
They said the OnePlus website was using the Magento eCommerce platform which has been hacked in the past.
After going through the payment process on the site, the Fidus researchers said they had found that the payment page, where customers are asked to enter their card details, was hosted on-site, and was not an iFrame by a third-party payment processor.
"Whilst the payment details are sent off to a third-party provider upon form submission, there is a window in which malicious code is able to siphon credit card details before the data is encrypted."
Has OnePlus' checkout page been compromised?https://t.co/7cRGwz6Cjl— Andrew Mabbitt (@MabbsSec) 14 January 2018
The Fidus researchers said two issues were noticed with the site: OnePlus did not appear to be PCI-compliant and this was not mentioned on their website.
Additionally, the company claimed that it did not handle credit card payments when, in fact, it did.
They pointed out that Magento hacks had been detailed in 2015 by a company known as Sucuri.
Fidus said that the second method was by modification of the Cc.php file; however, this required shell access to the server and indicated a serious compromise.
Thirty-nine users on the OnePlus forum have complained about credit card fraud on the UK website.
Both OnePlus and Fidus have been contacted for comment.