A hacker broke into the child-support computer system run by the state Treasurer's office and may have obtained names, Social Security numbers and other information of 300,000 people and 9,000 employers.
Treasurer Ron Ross announced the security breach Thursday.
The system helps collect and disperse child-support payments.
The hacker got into a back-up computer server Wednesday morning for about 40 minutes and launched a virus, which Ross said was immediately removed.
Ross said the hacker was "probably from outside the United States."
He said he did not believe any information was downloaded but that the State Patrol is launching a computer forensic investigation of the incident.
The computer network also contained tax identification numbers for 9,000 businesses who collect and send in child-support payments to the Treasurer's Office.
"Until we know for sure, I encourage all parents who pay or receive, and all employers involved, to monitor their accounts and report unusual activity," Ross said.
Ross said letters will be sent as soon as possible to potentially affected persons informing them of the breach and providing information about identity theft protection.
Ross said the attack appeared to be routed through Australia from Asia.
"There are very smart and bad people out there," Ross said. "We do not know if that person was able to download any information."
Ross said his office immediately put tougher security measures on the system.
More than $233 million flowed through the system last year, totaling 1.5 million payments, by check or electronic deposits.
The computer system was launched in December 2001 and has processed more than $1 billion in child support payments to 176,000 children.
Creation of the Nebraska Child Support Payment Center was mandated by the federal government. Nebraska officials worked under a Dec. 31, 2001 deadline to get it operational, or face a $5 million fine.
Under the old system, Nebraska and most other states handled child support at the county level. But the counties generally could not share information and businesses faced the hassle of mailing checks to scores of offices. Federal law was changed to require states to install statewide computer systems.