Most laptops today have a built-in camera above the display. And most of those have a small light next to them that is supposed to turn on to alert the user when the camera is active. But a couple of years ago, researchers discovered that this doesn't always work; hackers can activate the camera on certain MacBook models (and probably some other laptops) without enabling the light and tipping off the user.

Ever since writing that story, I've had a precautionary Post-it Note over my laptop's camera. Newly minted presidential candidate Rand Paul is using concerns over laptop camera privacy to promote his campaign:

Paul's campaign has dubbed this the "NSA Spy Cam Blocker," urging supporters to "stop hackers and the NSA with this simple camera blocker."

I don't think there's been any proof that the NSA spies on people using webcams, but this isn't a crazy concern. We've known since 2013 that the FBI had technology to remotely activate targets' webcams and stream images back to the authorities.

Private-sector creeps have also jumped on the camera-hacking bandwagon in recent years. There's a whole underground community of men who trade tips and software for hacking into young women's laptops to capture naked pictures of them.

So Paul's webcam protector is a savvy bit of marketing. It provides a useful service (though a small Post-it Note will do the same job for a lot less money) and underscores an important theme of his campaign, while its prominent position above supporters' laptop screens will constantly remind them of his candidacy.