In the latest blow to Switzerland's centuries-old banking practices, the country's oldest bank pleaded guilty to a criminal conspiracy charge in the US on Thursday and admitted that it helped wealthy Americans for years avoid tens of millions of dollars in taxes by hiding their income from secret accounts abroad.

Wegelin & Co, founded in 1741, is the latest Swiss bank to reach a deal with US prosecutors as they crack down on Americans who kept their money in secret accounts overseas and the entities which helped them. Three Wegelin bankers also were charged criminally in the US last year.