US brand-owners using the social networking site say tracking software shows clicks on their ads are between 20 per cent to 100 per cent lower than the amount they are being charged.
"Facebook is simply stealing 20 per cent of clicks that I paid for, which adds up to thousands of dollars," posted one disgruntled advertiser on .
The social networking site has responded to the mounting complaints, with a spokesman insisting it takes click fraud "very seriously".
"Over the past few days we have seen an increase in suspicious clicks," he said. "We have identified a solution which we have already begun to implement. In addition, we are identifying impacted accounts and will ensure that advertisers are credited appropriately."
The complaints being levelled against Facebook are different to those search engines have had to deal with for years. In standard cases, bots rack up fraudulent clicks that never amount to a purchase or any other action.
However, in this case advertisers are claiming that Facebook is charging for clicks that don't exist at all, even from unscrupulous bots.
A recent report by the Click Fraud Index run by Click Forensics shows that click fraud reached its highest ever point in the fourth quarter of 2008.
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