Thousands of Coloradans may have had their information leaked due to a security breach on CodeRED — a emergency notification system used by various metro agencies.

CodeRED by Crisis24, a company based in Maryland, sent a letter to users on Friday stating that the system was part of a “targeted attack by an organized cybercriminal group… We have learned that data associated with the legacy OnSolve CodeRED platform was removed from our systems. While there is currently no indication that this data has been published online, we are proactively informing you that it may be leaked.”

The mobile emergency alert service has thousands of registered phone numbers in Colorado.

There are “88,000 landlines that are opted in to CodeRED and about 130,000 cellphone users, so anywhere between 30-50% of our county population is opted in to this system,” Douglas County Sheriff’s Office division chief of support services Taylor Davis told The Denver Gazette’s news partner, 9NEWS.

CodeRED is used by the Douglas County Sheriff’s Office, Weld County Sheriff’s Office, Thornton Police Department and Adams County.

Adams County, whose emergency dispatch center uses CodeRED, was not impacted by the security breach, but the others were, leading to the Douglas County Sheriff’s Office ending its contract with the system.

“The Douglas County Sheriff’s Office and 911 Board have taken immediate action to terminate our contract with CodeRED. We are working to secure a replacement system,” the office said, adding that emergency alerts will still be pushed out to residents through FEMA’s Integrated Public Alert and Warning System and social media.

“There is no evidence the stolen data has been published, but users are encouraged to monitor their credit and protect personal information,” the office added.

“It appears that the impacted dataset may contain contact information of OnSolve CodeRED users: name, address, email address, phone numbers, and/or associated passwords used to create user profiles for alerts,” Crisis24 said.

Davis added that dispatchers noticed something was wrong with the system when they couldn’t access it Nov. 10.

“Just about a month ago, we did pay almost $65,000 contract to CodeRED,” Davis said. “The legal team for the 911 board is working on what this means for our contract. Will we get any money back? Are we going to try to fight to get money back?”

Both the Douglas County and Adams County said users should log in to CodeRED and update their passwords. If that password is used somewhere else, users should change those passwords as well.

Users should also check in with credit bureaus to confirm information hasn’t been compromised.

9NEWS contributed to this report.