Internet mogul Kim Dotcom said Thursday he was considering taking legal action against tech giants such as Twitter, Google and Facebook for infringing copyright on a security measure he invented.

Dotcom, who is on bail in New Zealand as US authorities seek his extradition in the world's biggest copyright case, said he invented "two-factor authentication", which many major sites have adopted as a security feature.

Twitter became the latest major player to introduce the measure on Wednesday following a series of cyber-attacks which saw hackers take over the accounts of high-profile targets such as media organizations and send out fake tweets.

"Twitter introduces Two-Step-Authentication. Using my invention. But they won't even verify my Twitter account?!," Dotcom tweeted.

"Google, Facebook, Twitter, Citibank, etc. offer Two-Step-Authentication. Massive IP (intellectual property) infringement by U.S. companies. My innovation. My patent," he added.

To back his claim, the 39-year-old posted a US patent describing the authentication process filed in 1998 by Kim Schmitz -- Dotcom's name before he legally changed it -- and published in 2000.

Dotcom said he had never sought to enforce copyright on his invention but was now reconsidering in light of the US case accusing him of masterminding massive online piracy through his now-defunct Megaupload file-sharing site.

"I never sued them. I believe in sharing knowledge & ideas for the good of society. But I might sue them now cause of what the U.S. did to me," he said.

However, he said a more productive approach would be if the tech giants helped cover his legal bills to fight prosecution under the Digital Millennium Copyright Act (DCMA), which he estimated would exceed US$50 million.

"Google, Facebook, Twitter, I ask you for help. We are all in the same DMCA boat. Use my patent for free. But please help fund my defense," he tweeted.

"All of our assets are still frozen without trial. Defending our case will cost US$50M+. I want to fight to the end because we are innocent."

The authentication process works by sending a text message containing a verification code to the user's mobile phone when they login, which must be entered to gain access to the account.

The US Justice Department and FBI want Dotcom to face charges of racketeering, fraud, money-laundering and copyright theft in a US court, which could see him jailed for up to 20 years.

He denies US allegations the Megaupload sites netted more than US$175 million in criminal proceeds and cost copyright owners more than US$500 million by offering pirated copies of movies, TV shows and other content.

The German national is free on bail ahead of an extradition hearing scheduled for August and launched a successor to Megaupload called Mega in January this year.