The websites of several leading nonstate media in Russia have been shut down by denial-of-service (DOS) attacks as Moscow prepares for an opposition demonstration against Vladimir Putin's return to the presidency.

The newspaper "Kommersant," the Ekho Moskvy radio station, the Dozd Internet television channel, and the news aggregator slon.ru all experienced crippling DOS attacks on May 6.

The media outlets are continuing to issue news updates through the social-networking sites Facebook and Twitter.