GEOFF BENNETT: President Trump's border czar Tom Homan announced today that roughly 700 immigration officers will be withdrawn from Minnesota after what he described as unprecedented cooperation from local law enforcement.

But about 2,000 agents are still expected to remain on the ground for what he described as targeted operations.

During an interview with NBC News today, President Trump was asked why he directed Homan to withdraw some of the officers and what he had learned from Minneapolis.

DONALD TRUMP: I learned that uh maybe we can use a little bit of a softer touch, but you still have to be tough.

These are crim- We're dealing with really hard criminals in Minneapolis and elsewhere.

GEOFF BENNETT: There continue to be real concerns about ICE's tactics.

William Brangham focuses on that part of the story.

WILLIAM BRANGHAM: That's right, Geoff.

Homan's announcement comes amid ongoing intense protests about the use of force by ICE agents and the fatal shootings by them of Renee Good and Alex Pretti.

But there's a whole other set of tactics that immigration officials are using to track suspects and protesters.

This growing surveillance arsenal includes facial detection apps and databases, cell phone trackers and drones.

For more on how this technology is being deployed on U.S.

streets, we are joined by Joseph Cox of 404 Media.

Joseph, thank you so much for being here.

You have been covering all these different technologies that ICE agents are using and how they're able to scoop up information about people without them really knowing what they are doing.

Let's talk about some of those technologies.

One of them is called Webloc.

Explain what that is, what it does.

JOSEPH COX, 404 Media: Yes, so Webloc allows ICE to track the location of mobile phones without a warrant, crucially.

Now, this data is not coming from the telecoms.

It is not coming from AT&T or Verizon or T-Mobile.

It is most likely coming from the advertising ecosystem behind ordinary apps on your mobile phone.

So Webloc allows ICE to draw a map around a particular neighborhood or a block or a general area and then see the location of all the phones in that particular place that the tool has data on.

They could follow it from that location to somewhere the phone stays overnight.

Presumably, that's where the person is sleeping and maybe where they live.

They can then follow it to their potential employer as well.

And again, crucially, it allows ICE to do this without a court order, without a subpoena.

They're just buying access to the data itself.

WILLIAM BRANGHAM: So if they knew my name or they knew that I was a particular person of interest, they can just scoop up that publicly available data, commercially available data, and then use it to track me?

JOSEPH COX: They would most likely do it based on a location.

So I do want to stress, we don't know exactly what ICE is using this for, but the tool has been marketed by the company that sells it to monitor things like the Black Lives Matter protest that we had several years ago.

What ICE would probably do is draw a map, draw a circle around a particular location, see the phones there, and then if those people or devices are of particular interest, they would then follow those and then figure out who that person might be.

WILLIAM BRANGHAM: I see.

Another one of these devices is called Paragon Solutions, which is a phone hacking tool.

What does it do?

JOSEPH COX: I mean, Paragon sells some of the most powerful surveillance technology that law enforcement and intelligence agencies are able to purchase.

It allows ICE or any government customer to remotely break into most likely fully up-to-date mobile phones.

Now, this is an exceptionally powerful capability.

It would allow ICE to read Signal messages, for example, messages which are usually encrypted, or all sorts of other data on the mobile phone as well.

WILLIAM BRANGHAM: It's really extraordinary that they would have that ability.

Another one called Mobile Fortify is somewhat similar to what people might have seen at airports when they go to check in for their flights.

What does that allow the government to do?

JOSEPH COX: So Mobile Fortify is ICE's and now Custom and Border Protection's facial recognition app.

An ICE officer can point their mobile phone at any person inside the United States.

It will then query a database of hundreds of millions of images and other government databases as well to verify whether this person has been given a deportation order, whether they're a citizen, bring up other personal information as well.

And we have seen both ICE and Customs and Border Protection using this tool on American streets, where, instead of going up to somebody and asking for their passport or other identification document, perhaps they don't want to hand that over, the DHS officials will just use this app to scan their face.

And, crucially, ICE argues and believes you cannot opt out of this scanning.

If ICE wishes to scan your face with Mobile Fortify, they believe that you must comply with that.

WILLIAM BRANGHAM: Is any of this legal?

I mean, anyone with even a cursory knowledge of the Constitution knows there's a prohibition against unreasonable searches and seizures.

I'm not a lawyer, but this certainly seems to fall right squarely in the middle of that.

JOSEPH COX: I think that's a really interesting thing about a lot of these surveillance technologies, is that it is a legal gray area, or, if anything, ICE might actually be acting legally as well.

When it comes to Webloc, the phone location data, they don't need a warrant because they're buying it from a commercial broker.

They don't need to go to a court and get permission to do that.

With the facial recognition staff from Mobile Fortify, they don't need to do that either, in their eyes, because they already have all of that information.

It is already querying all of these government databases.

Now, with the mobile phone spyware, yes, hopefully, ICE would get a warrant before deploying that.

When the FBI has deployed hacking tools in the past, they have sought a warrant as well.

But, again, the exact contours and context which ICE is actually using that technology is really unclear.

So, frankly, we don't know if they have obtained a warrant to use that.

WILLIAM BRANGHAM: How can people protect themselves from this?

I mean, we're not trying to shield people from being able to escape criminal activity or repercussions for it.

But if someone is legally protesting, is there anything that they can do to try to hold off some of these more invasive searches?

JOSEPH COX: Yes, I think that's the thing with Webloc especially, is that it's quite an indiscriminate tool.

This is not like it just includes the mobile phone data of criminal suspects.

I would just say that people should probably be cautious and vigilant about the apps they install on their phone.

If you install a video game, for example, and it asks for your location data, maybe take a minute and think, I don't know if that game really needs my location data, because ultimately you don't really know where that information is being transmitted to.

And it could end up in the hands of any other number of companies or potentially ICE as well.

WILLIAM BRANGHAM: Joseph Cox of 404 Media, thank you so much for being here.

JOSEPH COX: Thank you.

Really appreciate it.