A sum of $775,000 wouldn't pay for a year's supply of lattes at cash-rich Microsoft (MSFT). But that's what the company is seeking in a lawsuit against three Canadians for so-called click fraud. The allegation: that Melanie Suen, Eric Lam, and Gordon Lam—believed to be a mother and her two sons—have been clicking on ads on Microsoft Web sites for financial gain. The company thinks the family, which makes money on Web ads, may have clicked repeatedly on rival advertisers' links, thus boosting the fees they pay and depleting their budgets—which could result in higher placement for ads tied to the family. Experts say the suit could provide a much needed deterrent to such practices, which may make up more than 10% of all clicks on paid links.