Cyberattackers have hit the US Treasury Department, Secret Service, Federal Trade Commission and Transportation Department in a series of attacks that started on 4 July and disrupted operations.
South Korea's presidential Blue House, defence ministry, and National Assembly were also attacked, according to reports from Associated Press.
The attacks began three days after the Treasury froze the assets of four people it said provided direct support to al Qaida and Lashkar-e Tayyiba (LET) in Pakistan, and facilitated terrorist attacks, including the July 2006 train bombing in Mumbai, India.
The US Computer Emergency Readiness Team (US CERT), part of the US department of homeland security, warned of the attacks and provided advice to mitigate them.
Last month the UK and US governments announced plans to create "white hat" hacker teams to seek and destroy cyberattackers.
"The government can no longer stand by and suffer cyberattacks (such as infiltration via hacking and denials of service) without hitting back," Robert Hannigan, the prime minister's security advisor, said at the time.
The news comes after a stream of reports that cyberattackers were trying to infiltrate or disrupt government and private sector computer systems on both sides of the Atlantic.
Hannigan said the UK was relatively better off that the US because it had fewer government computer systems exposed to the internet.