A large percentage of mortgages are tied to the now shaky Libor rate banks charge to borrow from each other, according the Federal Reserve Bank of Cleveland.

U.S. and British officials launched recent investigations into more than a dozen banks after news surfaced that Barclays (BCS) manipulated the rate to report lower borrowing costs and higher profits.

Twisting those rates could have cost more than banks but many homeowners as well.

Roughly 45% of prime adjustable-rate mortgages are tied to the Libor index, and 80% of subprime ARMs are tied to it, according to the Cleveland Fed Economist Guhan Venkatu.

He analyzed data through May from Lender Processing Services (LPS), which covers roughly two-thirds of the mortgage market. Venkatu noted just 3% of the LPS data came up as subprime, so he used Mortgage Bankers Association numbers as well, which shows the subprime share closer to 10%.

"Libor has historically been the dominant index for subprime loans," Venkatu wrote.

More than 80% of subprime ARM originations were also linked to Libor in 2000, but by the time the housing bubble burst in 2008, essentially all subprime ARMs were linked to Libor as were half of prime loans.

A story in The Daily Mail showed it would be difficult for borrowers to prove they lost money on the Libor-fixing scandal, but that it may not keep many from filing lawsuits against the largest banks anyway.