Automattic CEO and WordPress co-creator Matt Mullenweg unleashed a scathing attack on a rival firm this week, calling WP Engine a “cancer to WordPress.”

Mullenweg criticized the company — which has been commercializing the open source WordPress project since 2010 — for profiteering without giving much back, while also disabling key features that make WordPress such a powerful platform in the first place.

For context, WordPress powers more than 40% of the web, and while any individual or company is free to take the open source project and run a website themselves, a number of businesses have sprung up to sell hosting services and technical expertise off the back of it. These include Automattic, which Mullenweg set up in 2005 to monetize the project he’d created two years previous; and WP Engine, a managed WordPress hosting provider that has raised nearly $300 million in funding over its 14-year history, the bulk of which came via a $250 million investment from private equity firm Silver Lake in 2018.

Speaking this week at WordCamp US 2024, a WordPress-focused conference held in Portland, Oregon, Mullenweg pulled no punches in his criticism of WP Engine. Taking to the stage, Mullenweg read out a post he had just published to his personal blog, where he points to the distinct “five for the future” investment pledges made by Automattic and WP Engine, with the former contributing 3,900 hours per week, and the latter contributing just 40 hours.

While he acknowledged that these figures are just a “proxy,” and might not be perfectly accurate, Mullenweg said that this disparity in contributions is notable, as both Automattic and WP Engine “are roughly the same size, with revenue in the ballpark of half-a-billion [dollars].”

Mullenweg has levelled criticism at at least one other big-name web host in the past, accusing GoDaddy of profiteering from the open source project without giving anything meaningful back — more specifically, he called GoDaddy a “parasitic company” and an “existential threat to WordPress’ future”.

In his latest offensive, Mullenweg didn’t stop at WP Engine, he extended his criticism to the company’s main investor.

“The company [WP Engine] is controlled by Silver Lake, a private equity firm with $102 billion in assets under management,” Mullenweg said. “Silver Lake doesn’t give a dang about your open source ideals, it just wants return on capital. So it’s at this point that I ask everyone in the WordPress community to go vote with your wallet. Who are you giving your money to — someone who’s going to nourish the ecosystem, or someone who’s going to frack every bit of value out of it until it withers?”

In response to a question submitted by an audience member later, asking for clarity on whether Mullenweg was asking WordPress users to boycott WP Engine, he said that he hoped every WP Engine customer would watch his presentation, and when it comes to the time when they’re renewing their contracts, they should think about their next steps.

“There’s some really hungry other hosts — Hostinger, Bluehost Cloud, Pressable, etc, that would love to get that business,” Mullenweg said. “You might get faster performance even switching to someone else, and migrating has never been easier. That’s part of the idea of data liberation. It’s, like, one day of work to switch your site to something else, and I would highly encourage you to think about that when your contract renewal comes up, if you’re currently a customer with WP Engine.”

‘A cancer to WordPress’

In response to the brouhaha that followed the talk, Mullenweg published a follow up blog post, where he calls WP Engine a “cancer” to WordPress. “It’s important to remember that unchecked, cancer will spread,” he wrote. “WP Engine is setting a poor standard that others may look at and think is ok to replicate.”

Mullenweg said that WP Engine is profiting off the confusion that exists between the WordPress project and the commercial services company WP Engine.

“It has to be said and repeated: WP Engine is not WordPress,” Mullenweg wrote. “My own mother was confused and thought WP Engine was an official thing. Their branding, marketing, advertising, and entire promise to customers is that they’re giving you WordPress, but they’re not. And they’re profiting off of the confusion.”

Mullenweg also said that WP Engine is actively selling an inferior product, because the core WordPress project stores every change that is made to allow users to revert their content to a previous version — something that WP Engine disables, as per its support page.

While customers can request that revisions be enabled, support only extends to three revisions, which are automatically deleted after 60 days. WP Engine recommends that customers use a “third-party editing system” if they need extensive revision management. The reason for this, according to Mullenweg, is simple — saving money.

“They disable revisions because it costs them more money to store the history of the changes in the database, and they don’t want to spend that to protect your content,” Mullenweg contends. “It strikes to the very heart of what WordPress does, and they shatter it, the integrity of your content. If you make a mistake, you have no way to get your content back, breaking the core promise of what WordPress does, which is manage and protect your content.”

TechCrunch has reached out to WP Engine for comment, and will update here when we hear back.