A coding error has been spotted in a video displaying the original source code for the world wide web, used to advertise a $5.4m (£3.9m) auction sale.
Creator Sir Tim Berners-Lee sold a non-fungible token - a certificate of ownership of a digital asset, of the code - through Sotheby's, on Wednesday.
The NFT included time-stamped files of the source code and an animated video of it being written.
The researcher who spotted the error said it looked like "a simple mistake".
Mikko Hypponen, from security company F Secure, said the symbols "<" and ">" had been translated into HyperText Markup Language (HTML) as "< >".
This was a tactic sometimes used deliberately to protect code - known as "escaping" - but in this case it appeared to have been done in error.
"There have already been discussions about whether this would make the NFT more valuable - like a postage stamp with a misprint error," he said.
Mr Hypponen added he had not personally bid for the NFT, which was sold to an unidentified buyer.
Website creator Mark O'Neill said it appeared "whoever made the video for the website ran the original text file through something that converted it into HTML".
"It's embarrassing for Sotheby's but I trust that nobody has done the same to the original code," he added.
Sotheby's and Sir Tim have been contacted by BBC News for comment.
The auction began on 23 June with an opening bid of $1,000.
Proceeds will go to charities chosen by Sir Tim and his wife.
Sir Tim created the world wide web, in 1989, by connecting different pieces of information on the early internet through hyperlinks.
He built the first web browser and server, refusing to patent his invention.
In 1993, Cern, the research organisation Sir Tim worked for at the time, relinquished all its rights to the technology and put it in the open domain.
And when the NFT auction was announced, Sir Tim told the Guardian: "The core codes and protocols on the web are royalty free, just as they always have been.
"I'm not selling the web - you won't have to start paying money to follow links.
"I'm not even selling the source code.
"I'm selling a picture that 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."