The official, who spoke on condition of anonymity, would not say who might have been responsible for the activity on what was described as an unclassified computer network used by employees of the Executive Office of the President.
The Washington Post cited sources as saying hackers believed to be working for the Russian government breached the unclassified computer network in recent weeks.
"In the course of assessing recent threats we identified activity of concern on the unclassified EOP network. Any such activity is something that we take very seriously. In this case we took immediate measures to evaluate and mitigate the activity," the White House official said.
The official said the technical measures to address the activity had led to limited access to some EOP network services. Some of the issues have been resolved, but the work continues.
"Our actions are ongoing and some of our actions have resulted in temporary outages and loss of connectivity for some EOP users," the official said.
A second administration official told Reuters there were no indications that classified networks had been affected.
The White House, like many government entities in Washington, frequently faces cyber threats.
© Thomson Reuters 2014
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