Just to make clear, election advertising has always been misleading, but it's never before misled people in totally different ways simultaneously.
Posters, newspaper ads, TV spots etc are the same for everyone who sees them, and everyone has a common frame of reference about the candidate.
With online ads personalised down to the individual level, everyone sees something different, but they don't know this is happening. This makes it much easier to deceive voters, and to distort elections.