By Ronald K. Henry
Family Law Quarterly of the American Bar Association, vol. 40, no. 1, Spring 2006
From the article:
If paternity fraud were a “one in a million event,” we might shrug and say that the random strike of paternity fraud is no worse than the random strike of lightning. The reality is that the lowest estimates of the number of paternity fraud victims [in the USA] are in the tens of thousands, and I believe that the number may be in excess of one million. The scandal is that the child support enforcement bureaucracy has consciously chosen to make no attempt to quantify the problem.
Ronald K. Henry
The full story, thanks to the Equal Justice Foundation, is accessible here.

Here is an update:
Ask Mr. Dad: Protecting yourself from paternity fraud
By ARMIN BROTT, McClatchy-Tribune News Service
Dear Mr. Dad: My wife and I are about to get a divorce. We have a 1-year-old boy and she’s pregnant with our second. Here’s the problem: She’s been having an affair for the last two years and I’m concerned that the children aren’t actually mine. What can I do to protect myself?…
Full Story: http://www.newsobserver.com/2172/story/1134629.html