Udemy, a platform for experts to sell educational courses, has been accused of not doing enough to remove stolen content from its service.
The site allows people to upload training materials and then charge Udemy users, of which there are more than seven million, for access.
But several experts and academics have expressed anger at finding their courses uploaded to the site and offered up for sale, without their permission.
Udemy, which raised $65m (£43.3m) in investment in June this year, responded by saying it relies on users flagging copyright infringing content and would review its procedures for doing so.
Rob Conery discovered that his programming courses had been reposted – but sometimes with identifying information intentionally removed.
"Piracy happens," Mr Conery said.
"But I've never seen it rewarded so openly… so brazenly.
"I work really hard on these videos and someone just stole it and is selling it on Udemy."
Udemy had been selling one of Mr Conery's courses for $15 (£10) – discounted from the usual $24 (£16). The deal was also being promoted in a Facebook advertisement.
The course had a five-star rating, and has had 923 enrolments, worth almost $14,000 (£9,300) at the discounted price.
In response to the complaints, Udemy said it takes copyright claims seriously and removes courses that are flagged up by the community.
However, to report instances of copyright infringement, users must first join Udemy – an obstacle described as "sleazy" by Mr Conery. A separate support email can be used by non-members, but this method of reporting content is not publicised clearly on the site.
Computer security expert Troy Hunt also found his material posted on Udemy. A course about ethical hacking – also now removed – was being sold for $47 (£31).
The Udemy version was identical to a course Mr Hunt had posted on an alternative site – although the Udemy version had the words "Hi, I'm Troy Hunt" removed from the beginning of the course.
Also, he had found that watermarks on the slides had been blurred out.
After being contacted by the BBC, Udemy responded to complaints in a blogpost.
It said no money had changed hands from the sale of Mr Hunt's course "as the fraudulent instructor had created coupon codes to allow students free access to the course".
The company added: "As an open marketplace of online content, we, like other platforms, face bad actors that seek to profit by stealing intellectual property and reposting it as their own.
"This is in clear violation of our terms of use and against every principle we hold as supporting open marketplaces.
"Our escalation team will be meeting after the holiday to review all of our copyright processes, including allowing people who do not have a Udemy account to use our flagging notification system."
Follow Dave Lee on Twitter @DaveLeeBBC
Zelensky thanks 'ordinary Americans' as he meets Biden
Putin says Russia not to blame for Ukraine war
Powerful US storm disrupts holiday travel
The man who survived the 'Nazi typist's' concentration camp
African, Arab or Amazigh? Morocco's identity crisis
What to expect from next World Cup in 2026
The trip that transformed Australia and China ties
The two sides of Scotland's gender law debate
Ghost Town: 'The song Thatcher wishes was never released'
Ros Atkins on… China’s Covid surge. Video
What it will mean when Indians outnumber Chinese
Who could replace Elon Musk as Twitter boss?
The dark side of a children's classic
Asia's most beautiful train route?
The diseases soaring post-lockdown
© 2022 BBC. The BBC is not responsible for the content of external sites. Read about our approach to external linking.
