Navalny, in a letter addressed to Investigative Committee chief Alexander Bastrykin, said investigators might have shared passwords acquired during searches of his house and office with hackers to gather evidence for a possible criminal case against him

Navalny also said the hacking attack might have been a reprisal by “crooked officials” after he called on Bastrykin on Monday to check for misconduct by investigators.

"My e-mail has been broken into, and through that, my Twitter," Navalny wrote on his LiveJournal blog early Tuesday. “It's obvious it was [hacked] from the computers and iPads seized during the search."

Navalny's Twitter account was taken over by a foul-mouthed impostor who spewed insults at his supporters and claimed that he had been working for President Vladimir Putin all along.

The hacker also changed the account's avatar to a photograph of d'Artagnan, the hero of Alexandre Dumas' "The Three Musketeers," with the caption "You are all pedophiles, and I am d'Artagnan!" and a new profile description: "Crook and thief Alexei Navalny 2.0.”

Navalny published his appeal to Bastrykin on his LiveJournal blog and Facebook page, which were evidently not hacked into.

A notorious cyber hooligan calling himself “Hell” took responsibility for the break-ins and posted screen shots of the innards of Navalny's Twitter and Gmail accounts on his blog.

Navalny “is a thief, a crook and an informer, and on top of that, he lies constantly. That was reason enough for me,” Hell said in comments posted Tuesday on Izvestia’s website when asked why he decided to hack into Navalny's accounts.

Hell has been implicated in a string of recent attacks on opposition leaders' e-mail accounts and blogs. In October, he claimed to have hacked into Navalny's e-mail account, leaking hundreds of personal e-mails onto the Internet.

The hacker railed against Navalny in a blog post that briefly appeared on the Public Chamber's website last month. The post, written in a squeaky-clean style unseen on Hell's profanity-laced blog, was quickly removed, but not before fueling speculation about whether the hacker had links to the government, a claim Hell denied in the Izvestia interview.

Hell also has been linked to a hack of Boris Akunin's LiveJournal blog in December, replacing the opposition writer's image with the same photograph of d'Artagnan used Tuesday.

In a statement Tuesday, the Investigative Committee denied involvement in the hacking attack and accused Navalny of attempting to “pressure and discredit” an investigation into clashes between protesters and riot police at the “March of Millions” on May 6.

Navalny and other opposition leaders have been repeatedly questioned as witnesses in connection with a criminal investigation into violence at an opposition rally on May 6.

On Tuesday, Navalny was questioned about extremist slogans chanted at rallies on Dec. 5 and 24, his spokeswoman said on Twitter.

Opposition activists have long accused law enforcement officials of colluding with cyber criminals and yellow journalists.

Photographs of a cash horde seized by investigators in opposition-minded television host Ksenia Sobchak's apartment earlier this month appeared on the Kremlin-friendly tabloid Lifenews.ru shortly thereafter.

Hacked e-mails belonging to Lilia Shibanova, head of the independent Golos election-monitoring group that has come under fire from Kremlin supporters, appeared on Lifenews.ru in December, days after her laptop was seized at Sheremetyevo Airport.

The authorities have denied wrongdoing, and nobody has ever been brought to justice in connection with the hacker attacks or leaks.