[Gorani:] Life under ISIS in Mosul is oppressive, of course. Defiance can seem unimaginable. As Iraqi troops move inch-by-inch to the ultimate goal of liberating that city, there are people working right now to undermine ISIS from within Mosul. In this exclusive report, CNN's Arwa Damon shows us a secret team of anti- ISIS fighters there.
[Damon:] Operating deep within the shadows of ISIS territory in Mosul is a network so secretive, even its own members do not know each other's identities. The letter "M" spray-painted on Mosul walls "M" for Mokawa, the resistant. The message to ISIS, "We are here. We are among you." The Mosul battalions watch for weaknesses in ISIS'defenses, carrying out hit and run operations, or waiting for a moment to strike isolated targets like this checkpoint on the outskirts of the city. This man, Abwahali is one of their liaisons. How did the Mosul battalions even managed to initially organize themselves? The same happened elsewhere. And by the end of 2014, the Mosul battalions had formed. Their weapons are basic what they found and hid in the city or what they snatched from ISIS.
[Isis. Damon:] They operate in two to three-man cells, independent of one another. No cell knows specifically of another. No fighter knows the name of more than two others. Abwahali calls the man he says is with the battalions in Mosul. He's speaking from an orchard just outside of the city. Talking on the phone is punishable by death.
[Damon:] The distorted voice in this video says they assassinated an ISIS fighter. The images then show what they say is the dead man's I.D., pistol, and suicide belt. And Abwahali says, they are providing for intermediaries, intelligence, and coordinates to the coalition. Here is the aftermath of a strike they say was based on their information. And they are waiting for what they call zero hour, distributing leaflets warning ISIS its end is coming. They are ready ready for the day the Iraqi army breaches the city. And they rally the people to rise. Arwa Damon, CNN, Erbil, Iraq.
[Gorani:] Fascinating to see these resistance fighters, essentially, inside Mosul. Now, to something completely different, many of you have iPhones. So you might find the very story the next story, I should say, very interesting. Apple is releasing an update to its phone. It happens every few months, usually nothing to be excited about generally speaking. This time, however, the new software contains a very big security fix. So you might want to update your software on your iPhone right away. Samuel Burke is here to explain why. So what are these vulnerabilities to the iPhone that we're just learning about?
[Samuel Burke, Cnn Business Correspondent:] We're just learning about them. And if you only remember one thing from this report, go and update your iPad or your iPhone because security researchers at the University of Toronto have identified three major flaws that allow third parties to get some incredible access to your phone. I just want to put a list up on the screen so people can see. These flaws will allow this third-party software to track or record all of your text messages, your e-mails, your passwords when you type them in, the cameras. Of course, they could take video, your microphones that could include Viber and WhatsApp calls, your phone calls through your normal line, and user movement so there is a.
[Gorani:] So your GPS basically.
[Burke:] Exactly, so it could know exactly where you are. So there is a patch out right now.
[Gorani:] Yes.
[Burke:] And I would very much want to do that. The committee to protect journalists.
[Gorani:] Yes.
[Burke:] .is saying journalists should do it right away especially dissidents.
[Gorani:] Let me understand this. So there are companies that sell software that allow any user with the software in hand to track phones, passwords, confidential information on an iPhone remotely?
[Burke:] Just think about that case.
[Gorani:] Is it remote or does someone have to have access?
[Burke:] So it's remote but they get access to your phone and then they can use it remotely. Think about the FBI. All of a sudden, they drop their case with Apple and said, well, we've figured out another way in. And most security experts believe that it was software from a company in the Middle East that allowed them to get into that phone. So what this group at the University of Toronto is alleging is that an Israeli firm called NSO Group, in this instance, was selling software to governments all around the world some governments that some people may consider good and some governments that some people may consider bad. And that this Israeli firm sold this software and that software was what was allowing some of these governments to get in. And they're alleging that many dissidents have been targeted. Now, NSO, this Israeli cybersecurity firm, has responded to us. In a statement, they told me via e-mail, the following. They said, quote, "The company sells only to authorized governmental agencies and fully complies with strict export control laws and regulations. Moreover, the company does not operate any of its systems. It is strictly a technology company."
[Gorani:] Yes. But then they sell the software. What about Apple, what are they saying?
[Burke:] Well, it does seem like Apple is acknowledging this by the mere fact that you and I have both gotten the updates on our phones. And they say this in the following statement, a spokesman telling us, quote, "We were made aware of this vulnerability and immediately fixed it with iOS 9.3.5." That's what is available on your phone and your iPad right now. "We advise all of our customers to always download the latest version of iOS to protect themselves against potential security exploits." But again, what this does, it all comes back to this famous FBI case with the San Bernardino attacker and making you think, if a company can get into your iPhone or they can allow one government in, they might be allowed to they might allow any or every government in.
[Gorani:] Well, certainly. All right, well, always these security and privacy issues with thought these devices, computers and the like. Thanks very much and to our viewers, update your software.
[Burke:] Absolutely.
[Gorani:] The man known as Mr. Brexit joins Donald Trump on stage, the U.K.'s Nigel Farage after the message of encouragement for Trump's supporters, coming up.