• NFTs are a type of digital asset designed to show that someone has ownership of a unique virtual item, such as online pictures and videos.
• The web NFT has been made by British computer scientist and web inventor Tim Berners-Lee.
• It includes original time-stamped files containing the source code written by Berners-Lee, an animated visualization of the code, a letter written by Berners-Lee on the code and its creation, and a digital "poster" of the full code.

LONDON – A non-fungible token of the original code for the World Wide Web has sold for $5.4 million in a Sotheby's online auction.

The auction finished at 7 p.m. London time on Wednesday.

NFTs are a type of digital asset designed to show that someone has ownership of a unique virtual item, such as online pictures and videos, or even sports trading cards.

The web NFT has been made by British computer scientist and web inventor Tim Berners-Lee.

It includes original time-stamped files containing the source code written by Berners-Lee, an animated visualization of the code, a letter written by Berners-Lee on the code and its creation, and a digital "poster" of the full code. They will all be digitally signed by Berners-Lee.

"NFTs, be they artworks or a digital artefact like this, are the latest playful creations in this realm, and the most appropriate means of ownership that exists," said Berners-Lee in a statement.

"They are the ideal way to package the origins behind the web."

In a bizarre turn of events, Berners-Lee appeared to talk down the significance of the NFT in an interview with The Guardian published last Wednesday after critics questioned whether the auction aligned with the values of the web. "I'm not even selling the source code," he said. "I'm selling a picture I made with a Python program that I wrote myself, of what the source code would look like if it was stuck on the wall and signed by me."

The auction for the NFT — titled "This Changed Everything" — commenced on June 22, with bidding starting at $1,000.

The proceeds will benefit initiatives that Berners-Lee and his wife Rosemary Leith support, Sotheby's said.

Some NFTs have sold for millions of dollars in the last few months.

In March, South Carolina-based graphic designer Beeple, whose real name is Mike Winkelmann, sold an NFT for a record $69 million at a Christie's auction. Jack Dorsey, CEO of Twitter, sold his first tweet as an NFT for $2.9 million later that month.

Earlier this month, a rare digital avatar known as a CryptoPunk sold at Sotheby's for over $11.7 million. Total NFT sales reached an eye-popping $2 billion in the first quarter of this year, according to data from Nonfungible, a website which tracks the market.

But there are signs that the bubble could be bursting, with sales of digital collectibles falling dramatically in recent weeks. Overall sales plunged from a seven-day peak of $176 million on May 9, to just $8.7 million on June 15, according to numbers from Nonfungible. That means volumes are now roughly back where they were at the start of 2021.

— Additional reporting by CNBC's Ryan Browne.