The California Department of Motor Vehicles says there's no evidence of a computer breach, but it's launching an investigation "out of an abundance of caution."
DMV spokesman Armando Botello said Saturday the agency was alerted by law enforcement to a potential security breach within its online credit card processing systems.
"There is no evidence at this time of a direct breach of the DMV's computer system," Botello said in a statement.
But the agency has opened an investigation, and was cooperating with state and federal authorities.
As part of the probe, DMV will review its systems and seek information from the outside vendor that processes credit card transactions and from credit card companies.
KrebsOnSecurity.com was the first to report the possible breach, which it says involved online payments from Aug. 2, 2013, to Jan. 31, 2014.
A spokesman from MasterCard said it was investigating reports of a potential breach at the California DMV. Seth Eisen said MasterCard's own systems have not been breached.
Eisen said MasterCard has sent out alerts to member banks. He advised consumers to review their accounts and contact their card issuer for assistance.
The DMV said it has increased monitoring of its website. Any affected customers will be notified, the agency said.