Updated

The Obama campaign's online donation system contains "major security vulnerabilities," a watchdog group reported Monday, suggesting the flaws could open the door to illicit foreign contributions.

The study by the Government Accountability Institute flagged security problems with a host of political websites, including the online donation pages for nearly half the members of Congress. The report, though, homed in on what it described as three major flaws in the Obama campaign's system for soliciting contributions -- claims the campaign later rejected as unfounded.

For one, the report said, the third-party owned Obama.com -- which redirects users to an official Obama campaign donation page -- has 68 percent foreign traffic, which would suggest a large amount of foreign traffic likewise heading to the Obama campaign donation page.. The site, according to the watchdog group, was bought by an Obama bundler in Shanghai, China.

"It's very clear the Obama campaign is the most successful and aggressive at online fundraising and they on a regular basis are submitting contributions or asking for contributions from people around the world," Peter Schweizer, president of Government Accountability Institute, told Fox News on Monday. "At the same time (they) have the basic lack of security on the back end."

The study also flagged the "absence of the industry standard" CVV requirement -- the requirement that users punch in the security code on their credit cards before purchases -- and it said it's unclear whether the campaign uses a separate anti-fraud system to check where donors live. The study also claimed the campaign used "active foreign solicitation" with email solicitations that go around the world.

The report raised concerns that small-dollar donations could be trickling in with little accounting of where they come from. Information on donations under $200 does not have to be disclosed.

An Obama campaign official, though, told Fox News the claims were "baseless," pointing to "robust safeguards" in place to prevent improper donations.

A campaign blog post further explained that the campaign does not accept donations from foreign nations, using an "address verification system" to confirm their legitimacy and manually reviewing any transaction flagged as potentially fraudulent. The campaign said it also requires a passport copy from anyone eligible to donate but listed with an address outside the U.S.

The campaign said the GAI claims "are more reflective of the group's politics than any grain of truth," citing the conservative background of the group's leaders.

According to the GAI report, Mitt Romney has raised $58 million in donations under $200 apiece, while Obama has raised $271 million.

Government Accountability Institute said that Romney's website, unlike Obama's, does require donors to enter in their CVV information. However, the study questioned Romney's use of foreign bundlers, noting the "full extent" of the Romney bundling network is not known because the Romney campaign has not disclosed that information.

The report showed 47.3 percent of House and Senate members with online donation pages also do not use the CVV requirement.