NEW YORK - Independent groups that do not disclose the identity of their donors spent $132.5 million to influence elections nationwide this year, accounting for about a third of all spending by outside groups in the 2010 election cycle, a report released Friday found.

The analysis by the office of New York City Public Advocate Bill de Blasio aimed to quantify how federal campaigns had been affected by the Supreme Court's ruling on Citizens United v. Federal Election Commission. The ruling, handed down in January, cleared the way for companies and unions to spend unlimited funds to influence elections, often using money from anonymous donors.

Groups including the U.S. Chamber of Commerce and the American Federation of State, County and Municipal Employees took advantage of the new rules, spending tens of millions on campaign ads in races across the country.

Other groups formed specifically to make use of the new rules spent lavishly as well, including the Republican-leaning American Crossroads and Crossroads Grassroots Policy Strategies, which were formed with help from former President George W. Bush's top adviser, Karl Rove.

De Blasio's office analyzed aggregate spending data filed to the Federal Election Commission, along with independent expenditure records. The office also conducted a more in-depth analysis on the 10 costliest Senate races in 2010.

Among the findings:

Anonymous or unlimited corporate spending allowed by the Citizens United ruling represented 15 percent of all federal political spending in 2010.

Spending allowed by Citizens United accounted for $85 million in all 2010 Senate races, $40 million of which went to the 10 costliest contests.

Ads paid for by groups soliciting anonymous donors were more likely to be negative than those paid for by groups that disclose their donors. Seventy-five percent of the ads paid for by anonymous donors were negative, as opposed to 54 percent of ads by groups that identify their donors.

Heavy spending by groups under Citizens United did not guarantee victory. In three of the most expensive Senate races, candidates won despite a heavy onslaught of Citizens United spending directed at them.