A program that gives coveted immigrant green cards to wealthy foreign investors was so susceptible to fraud and abuse that it was used by an Iranian network that sought to send banned high technology home and spread terrorism abroad, federal investigators said.

The EB-5 program was used by “a network involved in a series of international assassinations and terrorism operations” that also was “procuring a variety of goods for Iranian entities,” states an unsigned memo from U.S. Immigration and Customs Enforcement made public Thursday. The memo was written in response to questions asked by Janet A. Napolitano as homeland security secretary.

The memo called the EB-5 program a weak point in the nation’s immigration security because visa holders can become green card holders and eventually citizens — without going through the background checks that most prospective immigrants face. The program is designed to attract foreigners who pledge to invest in the U.S. economy.

The memo was made public by Sen. Chuck Grassley, Iowa Republican, in a letter to ICE acting Director John Sandweg asking a series of questions about the case.