The attacks involve a flood of computers all trying to connect to a single site at the same time, which overwhelm the computer server that handles the traffic.

Novaya Gazeta's website typically receives 70,000 to 120,000 unique visitors every day, Muratov said. But the attack was so strong that at one point the website got 70,000 visit requests every 14 seconds.

Muratov said the attacks aim to "discredit the public platforms which express alternative points of views." He said he believed the attacks are linked to Russia's 2011 parliamentary election and its presidential election in 2012.

LiveJournal, Russia's most popular blogging site, suffered sustained outage earlier this week. President Dmitry Medvedev, an avid blogger, on Thursday condemned that attack as "outrageous and illegal."

The onslaught on LiveJournal started with an attack on the blog of anti-corruption activist Alexey Navalny, Kaspersky Lab analyst Maria Garnayeva said on the company's website.

Novaya Gazeta quoted Kaspersky as saying the attack on its newspaper and on LiveJournal originated from the same source. The lab was not immediately available for further comment.