Experts Fear Flying Terrorist Robots

Interesting summary in DefenseTech.org, Terrorists' Unmanned Air Force

We are all at risk of attack from terroists by Unmanned Aerial Vehicles (UAV's). The technology is becoming cheap and availble to anyone.
The availability of remote control or remote targeting make them well suited for a surprise attack.
They can be made small and fly close to the ground so that they are not detected by radar.

From the article:

Eugene Miasnikov of the Center for Arms Control, Energy and Environmental Studies at MIPT, calls the UAV a suicide bomber on steroids, basically. Unlike a suicide bomber, a drone can easily penetrate security and threaten otherwise safe areas (eg the Green Zone) or reach crowded public places like sports stadiums. Dense crowds would lead to large numbers of casualties from fragmentation bombs, and an attack by multiple UAVs could cause panic and further injuries in the crowd. And don't even get us started about chemical, biological or ‘dirty bomb’ radioactive payloads.

Defense Tech: Terrorists' Unmanned Air Force