Only one time use.

Think of like world leaders, celebrities, ya know 😉. Are you gonna make them do some embarassing things, or illegal acts.

My answer:

spoiler

Take control of an NSA agent with access to the most powerful hacking tools, hack everyone’s phone, install a program that randomly have a popup at random intervals, the popup message says “I’m watching you”. This also tries to spread itself to any other phone it can connect to. Pure chaos 😈

Pretty sure I can do this in a minute, depending on how good the NSA tools are.