"I'm alive and well," Gorbachev late Wednesday told the website of Novaya Gazeta newspaper, using a blanked-out Russian expletive to describe his ill-wishers who he said were "hoping in vain".
His indignant response came after two Twitter accounts of the RIA Novosti state news agency posted news of the death of the first and only president of the USSR to sign off on a bloodless breakup of its empire in 1991.
RIA Novosti said that the Twitter accounts of its press centre and its German language news service were hacked into and that the false reports were online for only five minutes before the agency removed them.
The message, published in a screenshot on the website of Kommersant daily, was hardly convincing. It said that "Mikhail Gorbachev has died in the Shoko cafe in Yekaterinburg."
It added that Gorbachev died as he was talking to a maverick politician, Yevgeny Roizman, who is standing for mayor of the Siberian city, suggesting a political motive for the message.
RIA Novosti said it would ask the FSB security service and prosecutors to investigate the hacker attack.
Gorbachev said in his statement on the website of Novaya Gazeta, which he co-owns, that he suspected the hackers were "carrying out the orders of some authorities."
He said he had asked the newspaper to investigate who was circulating the rumours.
Gorbachev, 82, has suffered health problems and his spokesman said in June that he was in hospital for planned treatment of his diabetes.