Google already credits advertisers that are overcharged through click fraud, whereby scam artists repeatedly click through on advertisers ads to deliberately bump up charges. Sites are then paid for every click through generated.
However, the case, brought by Lane's Gifts & Collectibles in Arkansas State Court on behalf of all Google advertisers, alleges that the search engine had not taken into account the scale of the problem, leaving thousands of advertisers out of pocket.
In a statement, Google has now confirmed it has agreed a settlement with the plaintiffs that entitles advertisers with improper charges dating back from 2002 to make claims for reimbursement.
Previously advertisers could only make a claim during the 60 days prior to notifying Google.
Google said: "We have said for some time that we believe we manage the problem of invalid clicks very well... and believe that this settlement is further proof of our willingness to work together with advertisers to reimburse for invalid clicks."
It is expected that the final settlement will be lower than $90m as part of the sum will be used to cover legal fees.
Yahoo! was also named in the suit but intends to carry on fighting the allegations.
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