By David Lawder WASHINGTON (Reuters) -The U.S. Treasury last month repelled cyber attacks by a pro-Russian hacker group, preventing disruption and confirming the effectiveness of the department’s stronger approach to financial system cybersecurity, a U.S. Treasury official said on Tuesday. The Treasury has attributed the distributed denial of service (DDoS) attacks to Killnet, the Russian hacker group that claimed responsibility for disrupting the websites of several U.S. states and airports in October, said Todd Conklin, cybersecurity counselor to Deputy Treasury Secretary Wally Adeyemo. The …