Sentence:  Many jihadist plots have been <WSD>foiled</WSD> and the security apparatus is getting better, overall, at pre-empting those who would do us ill. But, they say, the nature of the threat and the terrorists' increasing use of low-tech, asymmetrical tactics such as hire vehicles and knives, make it all but impossible to stop every assault. 
Meaning of the word marked with <WSD> tags:  To prevent (someone) from accomplishing something.