A torrent of secret money is flooding into the leading presidential campaigns, with more than $118 million, or one-quarter of the total raised in this cycle, banked without disclosure of who gave the funds or where the donations originated.

The money is coming from hundreds of thousands of donations of $200 or less, which have been widely praised for democratizing the system for funding White House bids. However, the surge in low-dollar gifts has come at the cost of transparency, since federal law only requires campaigns to itemize donations when a donor gives more than $200.

However, one area of concern with the flood of donations, particularly those made online, is that foreigners could be weighing in illegally in an American election. Mr. Obama's Web site allows donors to choose an address in one of 227 possible countries or territories, including Iran, Iraq, Zimbabwe, and Yemen.