Security experts are doubtful of a claim by French media group Vivendi that a drive-by hacker spoiled its shareholder vote last week.

Chief executive Jean-Marie Messier claimed that hackers had tampered with the vote which would have granted a new stock option plan to company executives.

Messier has said that the wireless devices used for the voting were open to hacking.

He maintained that the hack was carried out by a small team armed with a transmitter/receiver, and that the perpetrators had detailed knowledge of the procedures and technical protocols of electronic voting.

But security experts have said that the hacker theory is unlikely because, if the vote was that controversial, Vivendi's management would have put extra protection into the system.

Manifest, a UK firm which monitors corporate governance and proxy votes, explained that, although hacking could not be ruled out, voting conducted by electronic remote control devices is increasingly reliable.

But Vivendi is convinced of its claim. "We are sure we had significant malfunctions. This incident is extremely serious. We have referred the matter to the police," it said.

Gary Jensen, principal consultant at IT consultancy Silversands, was reported in the national press as saying that a drive-by hack of this type was difficult to accomplish because the hacker would have to intercept thousands of transmissions at once and change some of them.

"It is possible, but it sounds dubious to me. Relatively simple security precautions can be taken to ensure that electronic votes go smoothly, but these are not always used," he said.

"You would expect e-voting devices to be protected or encrypted in some way. In that case, it would be a lot more difficult to crack."

Vivendi's board is expected to call a new shareholder meeting in June to put all the resolutions to the vote again.