Seven men now stand accused of plotting to bomb the Sears Tower. Authorities said another group planned to release a deadly gas into New York subway system. A college student was said to discuss attacks against oil refineries and military bases.
And that's just in the last few months.
The United States has avoided serious attacks since 9/11, and many in law enforcement say that's because of their aggressive action.
Here's a look at five alleged terror plots targeting the U.S. in recent years, and how they were foiled:
PLAN: Algerian Ahmed Ressam planned to drive from Canada to Los Angeles with bomb materials and blow up LA's busy airport on the eve of the millennium.
TIME: December 1999
HOW: Ressam was arrested in Washington state as he drove off a ferry from British Columbia. Agents became suspicious when he was nervous and evasive under questioning.
SOURCE: A federal court that convicted Ressam of the plot. He temporarily cooperated with the government.
PLAN: Richard Reid tried to detonate a shoe bomb onboard an American Airlines flight from Paris to Miami. A British man, Saajid Badat, allegedly conspired with him but apparently backed out at the last minute.
TIME: December 2001
HOW: Passengers subdued Reid, who was then convicted in the plot.
SOURCE: Reid himself, who pleaded guilty to eight charges including attempted murder. He's now serving a life sentence.
PLAN: Southeast Asian men would hijack a commercial plane by using shoe bombs to blow open the cockpit door, then take control and fly the plane into Los Angeles' tallest building, now known as the U.S. Bank Tower.
HOW: The plot was foiled when an unidentified Southeast Asian nation arrested a key al-Qaida operative.
SOURCE: President Bush in a speech in February
PLAN: Jose Padilla, a former gang member, arrived in Chicago after traveling to Pakistan and Afghanistan, and planned to target up to three high-rise buildings with a radiological "dirty bomb."
HOW: The federal government has said he received weapons and explosives training from members of al-Qaida, though it remains unclear how he was caught. He hasn't been indicted on "dirty bomb" charges.
SOURCE: The White House and federal prosecutors
NEW YORK SUBWAY
PLAN: Release cyanide gas into several New York subway cars, using a device made of Mason jars.
HOW: The plot was called off 45 days before it was set to occur by Osama bin Laden's second-in-command, Ayman al-Zawahri.
SOURCE: "The One Percent Doctrine," a new book by Ron Suskind, a Pulitzer Prize-winning former reporter for The Wall Street Journal.