U.S. authorities are on high alert one year after a terror suspect supposedly tried to blow up a U.S.-bound jetliner by smuggling a bomb onboard in his underwear.

Christmas 2009 saw Umar Farouk Abdulmutallab, a Nigerian with alleged ties to al Qaida, unsuccessfully attempt to set off an explosive device while en route to Detroit.

Government agencies are taking precautions for militants trying to attack over the Christmas and New Year holidays. While there is no way of telling whether an attack is imminent, some experts say the holiday season presents advantages to militants.

"(Terrorists) are hoping to take advantage of an overstressed commercial aviation fleet and use that to their advantage," said Fred Burton, vice president of intelligence at global intelligence company Stratfor.

Operationally, the high volume of passengers traveling during the holidays makes it difficult for the authorities to spot a militant operative and foil a plot, Burton said.

Extremists are also big on symbolism, and for those who planned last year's attack, Christmas symbolizes its anniversary.

Fears of an attack also come amid recent warnings that extremists could try to poison salad bars in U.S. hotels and restaurants during this holiday season.

HOMEGROWN MILITANTS

In an interview on ABC channel's "Good Morning America" news show on Tuesday, Attorney General Eric Holder expressed concern over the possibility of attacks against the United States by radicalized Americans. Near the top of his list of worries is U.S. citizen Anwar al-Awlaki, a radical cleric who is believed to be laying low in Yemen.

With terror networks under close scrutiny from the United States and its allies worldwide, organizations such as al Qaida are wary of conducting large-scale operations such as the 9/11 attacks. Extremist groups' funds have dwindled and training skilled operatives is a difficult endeavor under the watchful eye of the U.S. intelligence, experts say.

As a result, militant groups are now focused on recruiting Americans to conduct smaller-scale attacks, which might include, for example, targeting shoppers at a mall with a pistol. Such an operation is cheap, requires little skill or planning and has already been successfully pulled off.

Last year, a U.S. Army psychiatrist went on a shooting rampage at Fort Hood, Texas and killed 13 U.S. soldiers. The shooter, Nidal Malik Hasan, allegedly has ties to al Qaida's Yemeni branch.

Another advantage is that U.S. citizens have no language or culture barriers and are familiar with local geography.

WHEN WALLS GO UP, TERRORISTS SEEK A WAY AROUND

U.S. transportation authorities have in recent months implemented a new pat-down procedure and, in some airports, set up video imaging equipment to scan underneath the clothes of passengers.

But critics say there is no evidence that the initiatives make passengers safer.