In a stinging blog fussilade, Matt Mullenweg, the creator of the popular website-building platform WordPress, is accusing the Israeli company Wix of improperly copying WordPress code without giving it credit. And in a friendly defense, Avishai Abrahami, Wix’s CEO, denies it.

Mullenweg levelled the accusations on Friday, saying the publicly traded do-it-yourself web building service copied WordPress’ editing function in a product it launched earlier this month that allows users to do things like change content on their sites over their smartphones in real time.

The WordPress code is in open-source, which means anyone is free to use it, but Mullenweg said Wix failed to give WordPress proper attribution and didn’t adhere to the terms of the general public license that governs open-source software.

“Wix has always borrowed liberally from WordPress – including their company name, which used to be Wixpress Limited. – but this blatant rip-off and code theft is beyond anything I’ve seen before from a competitor,” Mullenweg wrote.

Abrahami said he was shocked at this accusation. “Wow, dude I did not even know we were fighting,” he said in a post on Sunday and offered to sort out any misunderstandings. “I believe in friendly competition, and as much fun as it is to chat over the blogosphere, maybe we can also do it over a cup of coffee?”

“Yes, we did use the WordPress open source library for a minor part of the application (that is the concept of open source right?), and everything we improved there or modified, we submitted back as open source,” he said. “Our product was always called Wix and our website Wix.com, we never borrowed from your marketing or brand.”

Wix shares ended down 0.2% at $41.20 on Friday.

Haim Ravia, senior partner and head of the Internet, cyber and copyright group at the law firm Pearl Cohen Zedek Latzer Baratz said that even open-source software can come with conditions, for example GPL software requires people using it to preserve its terms and not charge others for modified versions. But, he added, he wasn’t familiar with the WordPress-Wix dispute

“Matt contends, and I’m assuming he’s telling the truth, that Wix copied the code and failed to meet the terms of the license,” said attorney Jonathan Klinger. “If it’s true, then Matt, as one of the developers, could demand compensation, but could also be entitled to parts of the Wix code. If it’s not true, then Matt could be risking a lawsuit.”

He said that similar cases have usually ended with the latter option as a settlement.