Criminals and terrorists may take weeks or months to collect the information they need to plan an operation. They usually use the easiest methods and sources of getting information early in the planning stages to minimize the risk of their operation being compromised. If we understand how information can be collected by the bad guys and used against us, we can take steps to protect the information that we determine is critical.
What are some of the sources and methods criminals and terrorists use to collect intelligence?
Please use .gov sites or scholarly sources for references.