Novaya Gazeta's web site was paralyzed by a hacker attack for a sixth day Sunday in what editors called the strongest assault ever to hit the opposition newspaper's online edition.

The denial of service attack started Tuesday morning and peaked Thursday when the site recorded 1.5 million visits per second, said Sergei Asriyants, the newspaper's web editor.

"We had hacker attacks before but never as strong as this," he told The Moscow Times.

The attack was weaker Friday but still too strong for the newspaper's server, he said.

Novaya Gazeta's stories continue to appear online on the paper's live journal site at Novayagazeta.livejournal.com.

Asriyants could not say where the attack had originated or who was behind it but acknowledged that it was well organized.

"The only thing I can say is that this is not the job of amateurs," he said.

The Russian Internet was awash with speculation over the weekend of what had triggered the attack and who was to blame. One widely circulating theory was that it was motivated by a commentary by Yulia Latynina published in Monday's Novaya Gazeta. Latynina is also a Moscow Times columnist.

In the articled titled "Bee Cluster or Anti-Baker," Latynina argues that Russia is so corrupt that even Adam Smith's invisible hand does not work as a regulating force.

Latynina said by telephone Friday that she had no evidence that her article was to blame. But, she said, a hacker attack over her article would confirm the article's premise that corruption is uncontrollable.

"Maybe someone is just spending his royalties now," she said in regard to the hacker attack.

But Novaya Gazeta spokeswoman Nadezhda Prusenkova dismissed the possibility of a connection to Latynina's article, noting that it had been online a whole day and spread widely on the Internet before the attack started.

"Maybe someone just wants to punish us for our overall work," she said.

Novaya Gazeta asked law enforcement authorities to open a criminal investigation Friday.

"The complaint went to the Interior Ministry, the prosecutor general and the Federal Security Service," Prusenkova said, adding that no answer could be expected from the agencies before Monday.

Phone calls to the Interior Ministry's press service went unanswered Friday, but the ministry said Thursday that it would investigate the attack once it received a complaint.

Prusenkova said she hoped that the problem would be solved by Monday.

Novaya Gazeta is frequently critical of the government, and four of its reporters have been killed since 2000, including Anna Politkovskaya.

The newspaper is co-owned by businessman Alexander Lebedev and former Soviet leader Mikhail Gorbachev. Lebedev did not return a request for comment Friday.

Hackers have troubled national media organizations in the past.

In late November, a mystery virus destroyed the web site of Moskovsky Komsomolets. Editors of the popular national tabloid determined that hackers were behind the attack, which deleted parts of the paper's archive.

The government has been accused of orchestrating denial of service Internet attacks, including assaults on Georgian sites during the 2008 war in South Ossetia and on Estonian government sites in 2007. The Russian government has denied wrongdoing.

Russia has produced an active generation of computer engineers in recent years, and the country's hackers have achieved worldwide notoriety. Antivirus software firm Kaspersky Lab said last week that while most cybercrimes originated in China last year, Russians deserve the “gold medal” for Internet fraud.