The campaign to improve security at U.S. embassies and installations around the world has cost U.S. taxpayers billions and continues to leave American diplomats vulnerable - evident in the sudden "fiery and furious" attack on the U.S. Consulate in Benghazi on Tuesday that killed U.S. ambassador to Libya J. Christopher Stevens and three other U.S. government employees.

The attack was the second Tuesday on U.S. facilities in the Muslim world. Earlier in the day a mob descended on the U.S. Embassy in Cairo, scaled its high walls, tore down and destroyed its large U.S. flag, and attempted to replace it with a black flag inscribed with the Islamic shahada, "There is no god but Allah and Muhammad is his messenger."

The attacks allegedly stemmed from a film that was reportedly made in the United States by an Israeli-American real estate developer, Innocence of Muslims. Its trailer, widely viewed on YouTube, portrays Christian characters ridiculing Muhammad and his birth as a "bastard." In addition to the killings in Benghazi, U.S. diplomatic facilities in Morocco and Tunisia came under protest and attack over the film.

In 1998 after al-Qaeda-linked bombings in Kenya and Tanzania that destroyed U.S. embassies and left more than 200 dead, the Clinton administration requested $3 billion over five years to beef up security and infrastructure at U.S. embassies. Military experts, notably retired Adm. William Crowe, former chairman of the Joint Chiefs of Staff, protested that the funding wasn't enough. After the attacks on the United States on Sept. 11, 2001, the Bush administration agreed.

Over the next decade every American embassy around the world had to be retrofitted - and in some cases relocated and rebuilt - to comply with new standards that require a substantive setback from major roads and a security cordon that includes high walls and monitored entrances. In Nairobi, that meant moving the U.S. Embassy out of the downtown area to its present suburban location.

But the most dramatic example of beefed-up diplomatic security is the embassy in Baghdad, which opened in 2009 and cost $750 million to build. Like other U.S. diplomatic facilities, it combines multiple branches of the U.S. government in 21 buildings over 100 acres of downtown Baghdad real estate, and is more accurately described as a complex. The price to maintain its operation: $6.5 billion per year.

Investigators will question how two also-large and security-conscious diplomatic compounds - located in conflict-torn countries - so quickly became overwhelmed by mobs. News reports on Wednesday suggested only Libyan nationals guarded Ambassador Stevens, and Marines who normally provide protection were sent in only after the violence broke out. Following the attacks, 50 Marines were ordered to Libya to protect U.S. personnel there, and diplomats in Benghazi were evacuated to Tripoli, the capital.

"Make no mistake. Justice will be done," said President Obama in a Wednesday afternoon appearance at the U.S. State Department. Stevens, 52, is the first U.S. ambassador killed since 1979. By late Wednesday the State Department had identified only one of the three other employees killed: Sean Smith, an Air Force veteran who had worked as an information management officer for 10 years at other U.S. posts. "We are still making next of kin notifications for the other two individuals," said Secretary of State Hillary Clinton.

With the violence taking place on the 11th anniversary of 9/11 al-Qaeda attacks on the United States, investigators also are considering that protests over the movie could be a cover for a planned terrorist assault.

The film was allegedly produced and directed by Sam Bacile, who's been described as an "Israeli Jew" living in California and a 56-year-old real estate developer. But film consultant Steve Klein, an anti-Muslim activist in California, told The Atlantic's Jeffrey Goldberg that Bacile is a pseudonym. According to Klein, about 15 people made the film: "Nobody is anything but an active American citizen. They're from Syria, Turkey, Pakistan, they're some that are from Egypt. Some are Copts but the vast majority are evangelical."

Klein, founder of a group called Concerned Citizens for the First Amendment, has joined forces before with Middle Eastern Christians and others to protest Muslim activities. At an Orange County, Calif., rally last year his group carried a sign reading, "Muhammad is a child molester."

Klein also showed up to protest in Los Angeles last year after Los Angeles County Sheriff Leroy Baca went out of his way to show support for The Council on American-Islamic Relations (CAIR) and the Muslim Brotherhood. (See "Sound & fury," by Jill Nelson, WORLD Magazine, Oct. 22, 2011, issue.)