Bermuda-based Primus Guaranty Ltd has announced that its board of directors has approved an increase of $25 million to its buyback authorisation to repurchase outstanding common shares and seven percent senior notes due in 2036.The repurchases can be made from time to time in the open market or in privately negotiated transactions at prices and under the terms approved by management.The authorisation does not obligate the company to acquire any specific number of shares or senior notes in any period, and may be modified, suspended or discontinued at any time without notice.