The Utah Department of Transportation website for motorists paying electronic tolls to access Interstate 15 express lanes is back online after being shut down Tuesday over security concerns.

UDOT informed an estimated 21,000 express pass customers Friday that the site is safe to use following the installation of a security patch.

The site shutdown and update was sparked by one user’s discovery of a flaw that allowed access to others’ account information, including the last four numbers of credit cards, names, and mailing and email addresses.

“The vulnerabilty has been resolved,” Express Lane Website managers said in an email Friday to users.

After being informed of the security glitch Tuesday, Utah’s Technology Services Department, working with the Dallas-based vendor Etan Industries, conducted a “full forensic investigation” and “to this point has found no evidence of malicious attempts to access information,” the site managers said.

UDOT said the state will continue to monitor the website security to prevent future attempts to compromise the system. It also advised customers to regularly change passwords and security questions.