Swiss bank UBS has revealed that the authorities in the United States are investigating securities that it sold to wealthy clients which may violate US tax law.br br The probe is focused on so-called ‘bearer bonds’ which can be transferred without registering ownership, enabling the buyers to potentially hide assets.br br The bank said it was cooperating with investigators. br br The revelation was in its latest profit report which showed UBS paid out around one billion euros last year to US, British, Swiss and German regulators to settle various scandals. br br They included alleged manipulation of foreign exchange rates and claims it helped rich German clients dodge taxes.