Microsoft has cracked down on 25 UK-based computer firms selling PCs running on pirated versions of Windows.
The company had hired investigators to catch firms that were illegally installing pirated versions of Windows onto computers and selling them to customers.
Computer Weekly reports that the company has settled with 21 UK computer firms accused of piracy.
Investigators and whistle-blowers worked together to catch 4 UK firms selling pirated Windows and other Microsoft software from eBay accounts.
Consumers who purchased the fakes had thought they were buying software at a discounted price, but were being sold pirated software at huge profits.
In a statement, Michala Wardell, head of anti-piracy at Microsoft UK, said: “We attempt to deal with most offenders ourselves, but where sellers persist in illegal activities, we call in UK trading standards officers.”
"At a time when UK resellers are looking to expand their business post-recession, piracy not only impedes growth, but puts local hard-working computer shops out of business," he added.