Nokia has admitted hackers have cracked security codes on the N-Gage device, allowing its games to be played on other mobile phones.
The breach means games could be played on other mobiles
The protection system was supposed to stop games being copied and downloaded over the web.
"We have initiated an aggressive programme to stop the people behind these violations," a spokesman said.
Nokia said it would continue to work on improving its security codes for N-Gage, which was launched in October.
The N-Gage was released on 7 October amid much hype and a massive worldwide advertising campaign.
Nokia said it shipped more than 400,000 devices to retailers two weeks after launch.
Nokia said it had been "prepared" for attempts to break into the copy-protection codes, but it was still taking the breach "very, very seriously".
"This is not something the average consumer can do," said Nokia spokesman Damian Stathonikos.
"You need to have very specialised software tools and very specialised skills."
Mr Stathonikos said the company would work with net service providers to make sure the games did not appear for download on websites.
Rumours that the N-Gage gaming and mobile phone device had been hacked emerged on Tuesday on websites all over the world.
Now it has been confirmed, Nokia said it would have to move to protect its intellectual property rights.
As with most gaming gadgets, most of the money is made on the games themselves rather than sales of the devices.
The N-Gage is designed to compete with Nintendo's GameBoy, which dominates the portable gaming market.
It is estimated that more than $3bn will be spent on mobile gaming annually by the year 2007.