From the US Department of Defense:

"The threat posed by crude homemade bombs known as improvised explosive devices is growing and spreading across the globe, and will be the terrorists’ weapon of choice for decades, the commander of the Joint Improvised Explosive Device Defeat Organization said yesterday.

“We still need to do more,” Army Lt. Gen. Michael D. Barbero told the House Appropriations Committee’s defense subcommittee, adding that his organization is rapidly fielding critical counter IED capabilities. “But let me say up front that I believe the IED and the networks that use these asymmetric weapons will remain a threat to our forces and here at home for decades.”

These bombs, he said, will be the weapon of choice for terrorists because they are cheap and readily available. Bomb makers use off-the-shelf technology to make the deadly explosives.  IED’s were the number one killer of American troops during the war in Iraq."

Read more here.