The Internal Revenue Service this month will begin revising how it distributes Individual Taxpayer Identification Number cards (ITIN) to keep illegal immigrants from using them for fraudulent purposes. More than 6 million ITIN cards have been issued since 1996, but only 2 million tax forms have been filed using the ITINs. The status of the other 4 million ITINs is not known, but immigration-reform advocates say illegal immigrants are using the numbers to skirt U.S. immigration, tax and fraud laws. "The ITIN creates two problems: one for national security and one for identity theft," said a government source familiar with...