Google has proposed a $90 million (€75.4m; £51.7m) settlement of a class-action lawsuit over alleged click fraud.

The California-headquartered company has offered advertising credits to marketers who claim that for the past four years they have been charged for invalid pay-per-click fees and not reimbursed.

The suit, against Google and other search engines, was filed February 2005 in Arkansas by two small businesses. The settlement still has to be approved by a judge.

Click fraud occurs when individuals or machines generate clicks on ads that do not convert into any legitimate traffic to advertiser web sites.

It is difficult to trace click fraud, but in some cases it could be rivals of advertisers who seek to drive up their competitors' spending. Ad-hosting sites that get a cut of search engine revenue are also believed to use software and cheap labor to ratchet-up advertisers' payments.

Data sourced from; additional content by WARC staff