(CNN) -- Twitter users erupted in anger Saturday after discovering shirts listed on Amazon with a slogan that appeared to promote rape and violence against women.
The shirt read "Keep Calm and Rape On" and was available on Amazon's UK website. The company that prints the shirts, U.S.-based Solid Gold Bomb, removed the listing after it was notified of the slogan.
The company also removed a shirt with the slogan "Keep Calm and Hit Her."
Solid Gold Bomb apologized, saying the slogans were computer-generated and the company did not deliberately create them.
Founder Michael Fowler posted a message on the company's website saying he was "extremely sorry" for the issue.
"We simply do not produce poor humor or offensive products," Fowler wrote. "As a father, husband, brother and son, I would never promote such product in our company and it was clear to see this when looking across the millions of T-shirts that we offer or can produce on demand. Had these items ever sold, we would have immediately pulled the series and are doing so on our own and Amazon channels worldwide."
His explanation came too late for many on Twitter who called the shirts "disgusting."
"@solidgoldbomb 1/4 women will be the victims of sexual violence. Yay you for trivialising it so heinously," wrote @Seja75.
"When will industries take responsibility for messages they put into the world?" wrote Twitter user Kate Merrick.
Users also focused their anger on Amazon for listing the shirts. "Amazon fail," tweeted user Richard Machtel.
Amazon's spokesman in Britain, Ben Howes, gave a statement to CNN saying, "I can confirm that those items are not available for sale."
The shirts were never actually printed, explained Pete Ashton, a blogger in Birmingham, England, who writes about the Internet.
Companies such as Solid Gold Bomb offer slogans and designs for their apparel, and they are printed on demand when a customer orders one, he said on his site, iam.peteashton.com.
There are more than 540,000 Solid Gold Bomb items for sale on Amazon, which indicates they can't all be waiting in a warehouse for shipment.
"The shirts don't exist," Ashton writes. "All that exists is a graphics file on a computer ready to be printed onto a shirt if an order comes through. Still, you might say, someone had to make that file, to type those words and click save. Not necessarily."
Company founder Fowler says the slogans were started a year ago as a parody of the British wartime slogan "Keep Calm and Carry On," which was intended to encourage Britons to keep up their spirits.
Company computers created a combination of words that played off the slogan, taking into account character length and graphic resemblance to the original phrase, he said.
Said Ashton, "Yes, Amazon shouldn't be advertising these shirts. Yes, Solid Gold Bomb should have checked through their verb list before starting the algorithm. But as mistakes go it's a fairly excusable one, assuming they now act on it."
CNN's Per Nyberg in London contributed to this report.