Following the seizure in Europe of hollowed-out shoes containing blasting caps, U.S. authorities have been told to be on the lookout for thick-soled shoes that could be used to conceal explosives, as infamously was the case with convicted "shoe bomber" Richard Reid. According to a Department of Homeland Security-FBI bulletin issued Wednesday, Oct. 24, European authorities in September 2007 discovered a pair of shoes that were used to smuggle electric blasting caps across international borders for use in a terrorist attack. "A recent terrorist incident involving the international smuggling of electric blasting caps highlights the continuing use of modified footwear as a concealment method for explosive devices," stated the DHS-FBI Bulletin "Terrorist Use of Modified Footwear to Conceal Explosive Devices." Photos: Explosive Footwear "The shoes were modified in a manner that would make it difficult for security personnel to distinguish them from normal shoes visually." They were not worn, the bulletin said, but transported by bus concealed in luggage. "The shoes — made of leather with thick rubber soles — were modified so that the insole of each shoe could be removed for access to the hollow interior of the rubber sole," according to the bulletin. Click Here for Full Blotter Coverage. "Electric blasting caps were placed inside the hollow rubber sole, and the insole was glued to the rubber sole to appear as if the shoe was never modified," it continued. "The blasting caps — each measuring about two inches in length — were individually wrapped in paper, possibly to protect them from the glue used when the shoes were reassembled." The FBI told the Blotter on ABCNews.com that the bulletin was sent out as part of the routine information sharing between various members of the law enforcement and intelligence communities. "The FBI and DHS routinely send out these bulletins to our law enforcement and intelligence community partners to share information," said Senior Special Agent Richard J. Kolko, chief of the National Press Office. "It is not related to a threat, but is provided in order to allow officers on the streets to be alert to items that appear routine but may not be, as they go about their daily duties." The bulletin itself noted there was no "specific, credible" current threat information indicating "that terrorists plan to use this concealment method in the homeland." But it also noted the incident "highlights the continuing use of modified footwear as a concealment method for explosive devices." As such, the attempt to smuggle blasting caps is but the latest in a series of attempts by terrorists, whether autonomous or al Qaeda, to either smuggle explosive components in shoes, socks, gel bras and other items of clothing, or conceal complete improvised explosive devices in their clothing. The most infamous in recent years occurred on Dec. 22, 2001. On that day, Richard Reid boarded a Paris-to-Miami flight wearing a pair of dark-colored, high-topped shoes. Into the waffle-style soles, he had woven a high explosive and a length of detonator cord. He linked his device to a paper-wrapped, homemade, high explosive initiator. Alert passengers and crew members spotted him bending over in an attempt to ignite a fuse and subdued him. On Dec. 4, 2003, Reid was convicted in Boston federal court of attempting to use a weapon of mass destruction against U.S. citizens as well as on other charges. Reid, a 29-year-old British citizen, was sentenced in January 2003 to life in prison on three counts: one of attempted use of a weapon of mass destruction against U.S. nationals outside the United States and two of interference with flight crew and attendants using a dangerous weapon. He was also ordered to pay a $2 million fine and sentenced to consecutive 20-year terms on four other counts and a 30-year term on an eighth count. Since Reid’s attempt, airports in the United States have implemented a 100 percent X-ray inspection policy for footwear. The bulletin noted that some foreign airports do not, however, check all passengers’ shoes. In addition, terrorists have continued to refine their attempts to use footwear. But by the close of 2003, U.S. authorities issued another alert, one that was broadcast by ABC News TV and radio and published on ABCNews.com. That alert warned of terrorists using socks soaked in explosives and hung from a cord around a terrorist’s neck as a way to avoid bomb sniffing dogs and conceal the explosive from airport authorities. The bulletin featured a pair of blue socks it said were found by British anti-terror police in November of that year. They were discovered during a series of raids. Forensic tests on the socks allegedly found they had been laced with several explosives, including TNT, PETN (similar to Semtex) and RDX. "While it is not clear exactly in what capacity the individual may have been using the socks, it is possible the suspect may have been suspending the socks from around his/her neck or under outer garments in an effort to conceal explosives carried in them," said the bulletin. "It also cannot be discounted that these tethered socks were components of an improvised explosive device in the making. " At the same time the alert on the explosive soaked socks was issued, the FBI weekly circular to law enforcement warned that recent intelligence "indicates that terrorists continue to develop plans to hijack aircraft and use them as weapons" despite improved security and vigilance since the Sept. 11, 2001, attacks. In August 2006, a cell of al Qaeda-inspired and linked alleged British terrorists were stopped in the final stages of a plot to board a series of U.S. airliners bound from Heathrow to the U.S. and ignite their bombs in flight. Elements of the devices they planned to use were concealed in the bottoms of sports drink containers they intended to smuggle aboard. This post has been updated. Do you have a tip for Brian Ross and the Investigative Team?