The Saddam era Iraqi Intelligence Service (IIS) is still in business. In Arabic, the IIS was called the Jihaz al-Mukhabarat al-Amma, and was more commonly known as the Mukhabarat (Arab for Intelligence.) Combining the work of the American CIA, FBI and Secret Service, the IIS had a core strength of 5,000 highly trained, quite skilled, and very loyal (to Saddam) members. But the IIS controlled other intelligence and paramilitary personnel that totaled over 100,000 people. Few of these people were rounded up after Saddams government fell in April, 2003. They are still out there. Most of them anyway. Thusands have been arrested for involvement in anti-government activities, and hundreds have been killed while carrying out terrorist or intelligence operations. The IIS are almost entirely Sunni Arabs, and they are the core of the violence and terrorism the Iraqi government has had to deal with for the last 18 months. 

The IIS, a CIA report recently revealed, had several departments that specialized in developing weapons and tactics for the kind of war Saddam loyalists are fighting now. There was even one department that did nothing but develop road side bombs. These devices, which are assembled from various types of explosives (including artillery shells), and fitted into a large number of disguises (concrete blocks, trucks tires, piles of rubbish), were not a sudden inspiration, after Saddams defeat, of hostile Iraqis, but the deliberate invention of the IIS. 

It was discovered, shortly after Saddam was run out of office in early 2003, that the IIS had some kind of plan to keep on fighting. American intelligence personnel (military and CIA), slowly put together the details of the IIS plan. It wasnt just about designs for road side bombs, but also all manner of tactics and techniques on how to keep the fighting going. When Saddam was in power, the IIS also was in charge of smuggling goods into Iraq (past the UN embargo), and maintaining agents in neighboring countries to watch over these activities. That is why the flow of people, money and weapons from Syria appeared so quickly after Saddams was thrown out of power. The system was already in place. The Sunni Arabs dont just believe that they can use terror and violence to regain power in Iraq, they carefully planned how to do it while they were still in charge.