MADISON, Wis. – A company that provides electronic monitoring to track sex offenders, parolees and others said its system shut down after unexpectedly hitting its data storage limit, leaving authorities across 49 states unaware of offenders' movement for about 12 hours.

Prisons and other corrections agencies were blocked from getting notifications on about 16,000 people being tracked, BI Incorporated spokesman Jock Waldo said Wednesday. The system operated by the Boulder, Colo.-based company reached its data threshold — more than 2 billion records — Tuesday morning.

Tracking devices continued to record movement Tuesday, but corrections agencies couldn't immediately view the data. The company has substantially increased its data storage capacity and hasn't heard of any safety issues, Waldo said. People being monitored were unaware of any problems.

In retrospect, we should have been able to catch this," Waldo said.

BI contracts with about 900 government agencies across the country for monitoring and notification services, including real-time monitoring and delayed notifications about offender whereabouts. The agencies vary widely, and include state prison systems, sheriff's departments and pre-trial service entities, Waldo said.

In Wisconsin, prison officials had local police and probation agents detain about 140 sex offenders at local jails until the GPS tracking was back up and their whereabouts during the outage could be confirmed.

The offenders were never aware they weren't being tracked, state Department of Corrections spokeswoman Linda Eggert said. The shutdown affected about 300 people in Wisconsin, most of them sex offenders. She said the agency examined the offenders' GPS movements and was certain the shutdown didn't drive anyone to commit a new crime.

Along with GPS systems, the outage affected BI's in-home radio monitoring, typically used to check curfew compliance, and alcohol monitoring, which transmits data from home breathalyzer tests, Waldo said.

Before the shutdown, the company's database could hold 2.1 billion records, such as a GPS address or an alcohol reading, Waldo said. Company workers weren't aware of how quickly the database was filling up before it exceeded its limit, he said.

The company spent Tuesday expanding the threshold to more than a trillion records. Waldo said staff will work to develop a system that can supply early warnings as the database fills.

People in our development group knew there was a threshold," Waldo said. "They've never in their careers ... seen a system hit such a database threshold. It speaks of the enormity of the data we collect.

Waldo said he was unsure of all the different types of offenders or defendants the company tracks. The agencies that use the company's systems decide who they want to track, and contract confidentiality clauses prevent BI from disclosing the information.

Wisconsin prison officials said Wednesday it was the first time they had faced such issues.

Due to a system failure beyond our control, we faced a challenging and unprecedented event for our Electronic Monitoring Center," Wisconsin Department of Correction Secretary Rick Raemisch said in a statement. But thanks to the agency's emergency plan and cooperation from local law enforcement, "the situation was managed safely and efficiently with the number one priority being public safety," he said.

Eggert didn't know how many apprehension requests went out Tuesday or how many of the offenders remained in custody as of Wednesday.