Kwik Fit has confirmed that its computer network has been infected with malware, disrupting its ability to book in vehicle repairs and handle other customer requests.
It has since told the BBC that it is still experiencing some problems.
However, it declined to elaborate.
“We first experienced some issues with a virus in our IT network during the weekend,” said a spokeswoman.
“This affected a number of our systems but in the interest of ongoing security we can’t confirm the source of the problem.
“We have been working to get our operational systems back up and running normally and while there is still some disruption, our centres are open as usual.”
Several customers have sent messages to the firm via social media to express frustration.