HP has promised to reverse a software update which left printer owners unable to use third-party ink cartridges, apologising to customers for the lack of communication.

The software update left printers rejecting ink cartridges that did not contain a security chip made by HP, even if the printer had previously accepted the ink cartridges and printed perfectly acceptably. Worse, the update appeared to fire on a time-delay: it was shipped in March, but ink cartridges were only rejected in September.

HP has not explained why that delay, called a timebomb by some, was introduced. But the company has apologised in a blogpost for the lack of communication around the update – although not for the update itself.

“We updated a cartridge authentication procedure in select models of HP office inkjet printers to ensure the best consumer experience and protect them from counterfeit and third-party ink cartridges that do not contain an original HP security chip and that infringe on our IP,” HP’s chief operating officer, Jon Flaxman, said.

“The most recent firmware update included a dynamic security feature that prevented some untested third-party cartridges that use cloned security chips from working, even if they had previously functioned. We should have done a better job of communicating about the authentication procedure to customers, and we apologise. Although only a small number of customers have been affected, one customer who has a poor experience is one too many.”

The company says it will “issue an optional firmware update that will remove the dynamic security feature”, and expects it to be ready in the next two weeks. Users will be able to download it from the site.

HP did not express as much contrition for the overall aim of remotely disabling third-party ink cartridges, however, writing “we will continue to use security features to protect the quality of our customer experience, maintain the integrity of our printing systems, and protect our IP including authentication methods that may prevent some third-party supplies from working.” Third-party cartridges are frequently considerably cheaper than the brand’s own.

The reversal comes after an open letter from Cory Doctorow, of the Electronic Frontiers Foundation, which called on the company to apologise, roll back the update, and commit to never again distributing “anti-features” through the software update process.

“HP customers should be able to use the ink of their choosing in their printers for the same reason that Cuisinart customers should be able to choose whose bread goes in their toasters,” Doctorow wrote. “The practice of ‘tying’ is rightly decried by economists and competition regulators as an invitation to monopoly pricing and reduced competition and innovation. HP customers should choose HP ink because it is the best, not because their printer won’t work with a competitor’s brand.”