To use something in order to deliberately inflict harm on people is to weaponize it. If you start pelting your brother with grapes, he might accuse you of weaponizing your fruit salad.
When a group or government weaponizes something, they take an ordinary object and turn it into a weapon. This word was originally used during the Cold War as military jargon. When the U.S. Army added nuclear capabilities to rockets, preparing them for launching, they weaponized them. These days, it's common to describe everything from words to the internet as being weaponized — in fact, you can weaponize anything that can be used to attack someone else.