I think most of us kind of suspected this was going on, but NBC News has nailed down some solid examples and posed a valid theory that there’s plenty more of it that we never hear about. But is it illegal or even unethical?

The question at hand has to do with law enforcement using social media to infiltrate groups of people and check them out anonymously. They cite the example of the 2015 protests in Memphis, Tennessee following the police shooting of a black suspect. Local facebook accounts were blowing up with activists looking to meet up and take it to the streets. That’s when a new Facebook account belonging to “Bob Smith” showed up, looking to join in on the action and volunteering to take part in the protests. Over a period of three years, “Bob” was friended by numerous locals and invited to all manner of group chats and live protests.

But it turned out that “Bob Smith” was actually Detective Tim Reynolds of the Memphis Police Department’s Office of Homeland Security. He was keeping track of people in the Black Lives Matter movement. But it wasn’t just them. Reynolds was “joining” the social media circles of Confederate sympathizers, Klansmen, anarchists and potential troublemakers from across the ideological spectrum. And as NBC points out here, Reynolds was hardly a unique case.

Facebook is teeming with fake accounts created by undercover law enforcement officers. They’re against the rules — but cops keep making them anyway.

The proliferation of fake Facebook accounts and other means of social media monitoring ─ including the use of software to crunch data about people’s online activity ─ illustrates a policing “revolution” that has allowed authorities to not only track people but also map out their networks, said Rachel Levinson-Waldman, senior counsel at New York University School of Law’s Brennan Center for Justice.

She is among many scholars who worry that expanded social media surveillance could make people less likely to engage in online activities protected by the First Amendment, from sharing their opinions to organizing protests of the government. But there are few laws governing this kind of monitoring. Few courts have taken up the issue. And most police departments don’t have policies on how officers can use social media for investigations, according to Levinson-Waldman’s research.

“It’s pretty open territory,” she said.

So let’s return to the original questions I posed. Is this legal? Thus far there’s no law against creating a fake Facebook account, though it does violate their terms of service and the account can be suspended or deleted. It might be legally dodgy for the cops to do it, however. The Memphis PD is being sued by the ACLU (who else?) for supposedly violating a 1978 agreement that bans police from engaging in surveillance of lawful protests. We’ll see how that one works out.

But should it be prohibited in the first place? According to NBC’s law enforcement sources, pretty much every police department and federal law enforcement agency has at least one person who does this sort of social media surveillance. They try to embed themselves with known gangs, drug dealers and activists groups that might be causing trouble. They also lure in pedophiles and child pornographers that way.

We’re not talking about the cops hacking into your private messages and chats without a warrant. These are people’s public Facebook profiles. They send a friend request and you have the option to accept or decline. Do you really think all of your current Facebook friends are exactly who they claim to be?

I can see why people might be annoyed or even alarmed (if they’re doing something the cops would be legitimately interested in), but is that the fault of the police? You put all of your social media content out there for the world to see. And “the world” includes law enforcement. It may seem like stalking, but when it comes to monitoring potentially violent groups, stalking is kind of part of their job.