> The software may not be illegal, but particular uses of the software are

If you profit from selling software that is predominantly used for illegal purposes, or in the course of illegal activities, and you know it; you should be liable. Not put in jail. Not shut down. Just commercially liable.

This is a conservative test (commercial sale, predominantly illegal use, and wilfulness) and a conservative solution. In the long run, however, it balances commercial incentives with broader social ones.

We put thieves into prison because if theft were common it would increase distrust, society as a whole has an interest to fight theft, and we permit victims to sue the for restitution. In the same way society has a reason to put strict limits on surveillance.

There's the other problem: what damages can someone with a spy app on their phone ask for? There is no monetery value, they can at most ask for relief, that's not much of an incentive to stop.

> We put thieves in prison...In the same way society has a reason to put strict limits on surveillance

On one hand, we have a stylised burglar. On the other, a stylised lockpicking tool maker. The former is illegal; the latter is more complicated.

I am conservative about expanding the scope of the law. You criminalise surveillance apps in one decade and in the next, a security researcher disclosing a bug gets bitten.

> what damages can someone with a spy app on their phone ask for?

If someone snooped on my phone without my permission, they would see a lot of confidential client information. They may also see my and my loved ones’ protected health information. Finally, they will have sought and procured illicit access to my device, which is itself illegal. Lots of potential monetary damage in there, if only in legal time to ensure everyone who needs to be notified gets notified.

We've decided that privacy and freedom from surveillance is highly valued and deserving protection.

The target audience of that company is teenagers of helicopter parents. Whatever they have on their phones isn't privileged or valuable information, so the civil damages approach doesn't work too well. Some may have (against all advice) nudes on them, but I'd rather not wait until those are available to the public, and even then only those whose nudies escaped can sue.

The law needs to project the notion that privacy is valued, because it is highly valued. The only idea that I can come up with is to restrict availability of spyware. Others may have better suggestions.

My suggestion is to require spyware like this to put up an obvious indication on the screen of the device that spyware is active on it.

That still allows parents and employees, the supposed target audience, to use the software for its alleged intended purpose, but renders it useless for the illegal use cases.