"In recent weeks, four NOAA websites were compromised by an Internet-sourced attack," said Scott Smullen, a spokesman for the National Oceanic and Atmospheric Administration.
NOAA staff detected the attacks and responded immediately, performing maintenance on the sites, which were restored to full service, Smullen said in an email.
He did not identify the websites that were compromised or elaborate on the attacks but said they did not prevent the agency from delivering forecasts to the public.
The breach follows a string of attacks on government agencies including the White House, Office of Personnel Management and one of its main contractors, USIS, which performs background checks on U.S. government employees.
Most recently, the U.S. Postal Service said on Monday it was the victim of an intrusion that may have compromised the personal information of more than 800,000 employees, as well as data on customers who contacted its call center during the first eight months of this year.
The Washington Post reported that Chinese hackers were behind the NOAA attack, citing unidentified officials. The report said NOAA was forced to seal off data on disaster planning, aviation, shipping and scores of other uses.
Smullen would not comment on the source of the breach.
NOAA had a data breach last month when an agency employee in Ohio was charged with stealing sensitive information from a federal database for the nation's dams and lying about the breach to federal agents.
Xiafen "Sherry" Chen, 59, was arrested on October 20 at the NOAA office in Wilmington, Ohio, about 50 miles (80km) north-east of Cincinnati, the U.S. Attorney's Office for the Southern District of Ohio said.
Edited by NDTV staff from original story by Reuters