Websites of the New York Times and Wall Street Journal have experienced attacks.
Global cyber attacks against journalists and media organisations have increased over the past few years, according to the Committee to Protect Journalists.
According to the media rights group, criminal hackers offer an inexpensive and easy means of censoring the press agencies.
The media rights group said that cyber attacks including those on the New York Times, Wall Street Journal and Washington Post are part of a growing global trend.
Reuters cited Committee to Protect Journalists deputy director Robert Mahoney as saying that the group has seen distributed denial of service attacks against individual journalists and against individual news outlets increasing over the last few years.
"They are becoming increasingly sophisticated, it's very cheap to hire criminal hackers to mount such a distributed denial of service attack and digital security, information security is vital," said deputy diretor of the Committe to protect journalists, Robert Mahoney.
In early February, the websites of then New York Times (NYT) and the Wall Street Journal were reported to have been attacked by chinese hackers.
According to NYT, the hackers had continually breached its systems over four months and broke into the e-mail accounts of its Shanghai bureau chief, David Barboza.
Hackers have also infiltrated the Wall Street Journal's computer systems, in a bid to monitor its China coverage.
"We have reports in places in Africa and Asia of journalists coming under attack, even in North Africa, even before the 'Arab Spring' there were attacks against news outlets in Tunisia for example," Mahoney said.
"We have seen whole newspapers brought down in countries like Ethiopia because there's been an attack."