The companies said in a statement that over 21,000 suspect software sales were removed from the eBay UK site between August and October this year.
Around half were sales of counterfeit copies of Windows, and 36 per cent were fake copies of Microsoft Office.
Microsoft claimed that the crackdown is working because eBay removed 11,535 suspected counterfeit sales from the site in August. This fell to 4,460 in September and 5,423 in October.
But many sellers have insisted that eBay is not doing enough to tackle fraud. Richard Coleman, a regular eBay user from Luton, said: "I have been the victim of at least three fraudsters. One was a mobile phone that did not exist, another was a registration code for an online gaming service that was illegal, and the third was a pirated DVD.
"When you tell eBay they do not really help you. They informed us that the registration code we had was pirated but failed to recompense us for the cost.
"If I was buying software I would expect about 10 per cent to be pirated or fake. The only way you can tell is by comparing the pricing of a number of sellers. If it looks too good it is probably dodgy."
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