Experts say that vehicle attacks — whether IS-inspired or coordinated — present a unique challenge for law enforcement officials as they are nearly impossible to predict and easy to pull off. Charlie Winter, a senior research fellow at the London-based International Centre for the Study of Radicalisation and Political Violence, says what makes such attacks so frightening is the relatively low barriers to entry. Rita Katz, director of the SITE Intelligence group, says it is almost impossible for law enforcement agencies to stop IS-inspired attacks, especially vehicular-style ones like the one in London. Since 2014, this simple but effective method has been laid out repeatedly and in detail in IS propaganda material which continues to circulate online. In its November issue of its online magazine Rumiyah, IS extolled the virtues of the car as a weapon of attack and offered guidance to its followers, suggesting the Macy's Thanksgiving Day Parade as a possible target. Two weeks later, an Ohio State University student rammed his car into a group of pedestrians on campus and then got out and started stabbing people with a butcher knife before being gunned down by a police officer. While not much more can be done to boost security on the ground, more can be done to fight the spread of IS ideology online, and cooperation between European countries confronting this threat can be tightened.