New outside spending groups, dubbed super PACs, that can accept unlimited donations from corporations and wealthy individuals, spent $12.9 million in Iowa and other early GOP battleground states through New Year’s Day, according to an analysis of federal data.

The top beneficiary was former Massachusetts Gov. Mitt Romney. A total of $4.6 million was spent to help the nominal front-runner, the vast majority for ads torpedoing former House Speaker Newt Gingrich. Second was Texas Gov. Rick Perry, who benefited from $3.7 million in outside spending.

According to a Center for Public Integrity analysis of Federal Election Commission data,12 outside super PACs spent money, mostly on advertising, with the intention of electing or defeating a GOP presidential candidate. Ten have not yet reported their donors. The two that have did so last summer.

The upshot is that voters in Iowa, New Hampshire, South Carolina and Florida, all of whose contests will be held this month, won’t know who is paying for much of the advertising they see until after their votes are cast.

The next reports on donors aren’t due until January 31, the day of the Florida primary.

Federal court decisions in 2010 made it possible for individuals, corporations and labor unions to give unlimited contributions to political organizations (super PACs) and certain types of nonprofits, which can then spend the money to elect or defeat candidates. The groups are prohibited from coordinating their activities with candidates.

The top super PAC spender was "Restore Our Future" — the ambiguously named group set up to help Romney. The group spent $4.1 million, all of it in opposition to Gingrich, who enjoyed a brief lead in Iowa polls last month before the shellacking.

Restore Our Future has moved on from Iowa and spent $622,000 in Florida, a likely harbinger of more to come in that high stakes contest. Almost $100,000 has been spent by the pro-Romney group in South Carolina, whose primary is January 21.

Restore Our Future reported raising over $12 million in the first six months of 2011; it is apparently the best-funded of the new breed of PACs, and has received a few seven-figure donations. Not so well known is a second organization that hopped on the Romney bandwagon, Citizens for a Working America Inc.

The group spent $475,000 on a Christmas Eve ad buy praising the candidate.

The group initially supported Rep. Michele Bachmann of Minnesota but changed course shortly before the big ad buy.

The Center traced an address in an FEC filing for Citizens Inc. to the office of JSN Associates in Dayton, Ohio. The “JSN” is James S. Nathanson, who said Monday the group is “very definitely pro-Romney.” He would not say who the group’s donors are.

A previous incarnation of the group met with some controversy when it accepted a single $255,000 donation in 2010 from a Virginia consulting group called “New Models.” Questions were raised as to whether the group was being used as a pass-through for unnamed donors.

A super PAC supporting Perry, “Make Us Great Again,” spent all of its $3.7 million on ads backing the Texas governor.

Former Utah Gov. Jon Huntsman enjoyed the support of “Our Destiny PAC” which spent $1.9 million for ads in New Hampshire, where he opted to compete first rather than Iowa.

Two groups supporting Gingrich ponied up just over $900,000 for TV spots. The bulk of the pro-Gingrich spending was done by "Winning Our Future," a super PAC that was just started last month.

A surging Rick Santorum, a former U.S. senator from Pennsylvania, enjoyed $631,000 in supportive spending by outside groups.

"Priorities USA," a super PAC supporting President Obama, was also active, spending a little more than $306,000 on advertising opposing Romney.

And “Endorse Liberty Inc.,” a new super PAC embracing Rep. Ron Paul of Texas, spent more than $448,000, most of that on Internet advertising. It also listed one of the more unusual expenditures of the 2012 campaign — $2,000 on “costumes and makeup.”

Peter Stone contributed to this report.