Terrorist groups usually methodically plan attacks in advance, and may train participants, plant undercover agents, and raise money from supporters or through organized crime. Communications occur through modern telecommunications, or through old-fashioned methods such as couriers. There is concern about terrorist attacks employing weapons of mass destruction. Some academics have argued that while it is often assumed terrorism is intended to spread fear, this is not necessarily true, with fear instead being a by-product of the terrorist's actions, while their intentions may be to avenge fallen comrades or destroy their perceived enemies.