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Follow UsMedvedev's blog was the target of a "denial of service" attack on LiveJournal, a hosting website popular with government critics in Russia, where the Internet is a channel for popular discontent.
"I have received many appeals in connection with the ... attacks on LiveJournal. As an active user of (LiveJournal) I consider these actions revolting and illegal," Medvedev wrote in his blog here
"What has occurred should be examined by LiveJournal's administration and law enforcement agencies."
Medvedev is an avid Internet user and a champion of information technology. Russia has resisted placing restrictions on the Internet but analysts say hardliners in the government and security services would like to impose controls similar to China's.
In a February newspaper interview, an influential deputy of Prime Minister Vladimir Putin accused managers at Google of stirring up trouble in the uprising in Egypt which led to the departure of President Hosni Mubarak.
The website of the opposition newspaper attacked
The website of the opposition newspaper Novaya Gazeta (www.novayagazeta.ru) was the target of a "denial of service" attack on Thursday, anti-virus expert Alexander Gostev of the Internet security company Kaspersky Labs told Ekho Moskvy radio.
The site could not be accessed late on Thursday.
Russia's Internet is remarkably free and the home to often scathing criticism of Putin, Medvedev and the Russian elite.
LiveJournal hosts more than 4.7 million Russian bloggers.
Sup Media, the Moscow-based company that owns LiveJournal, said it was "delighted" that Medvedev had strongly criticised the attacks.
"We will continue to investigate the source of these attacks and work to improve our systems to prevent any recurrence," Sup Media CEO Annelies Van Den Belt said in a statement.