Ana Garcia reports.

We are all being watched. Security cameras track us as we walk down the street: Every purchase, bank transaction, email, text leaves a digital footprint.

But what if the most intrusive device of all turned out to be that cellphone in your hand?

Joshua Drake and Zuk Avraham are cyber-security experts who specialize in one thing: thwarting cyber attacks on mobile phones. Their company, Zimperium, in San Francisco, protects some of the biggest telecommunications companies in the world.

"I am always looking for new ways to hack mobile devices," said Drake.

And he found one: a security hole so massive, it scared even these seasoned hackers.

"I was terrified when I first found it," said Drake.

And now they are unleashing this cyber bomb on me to show Crime Watch Daily how dangerous it is. They've named this security flaw "Stagefright."

We won't reveal the details of this cyber attack because our mission isn't to help criminals, it's to help you protect yourself.

"Once we gain a foothold on your device, we can read everything on that device, so we can get all of your pictures and we can take new pictures on any of the cameras, we can listen on the microphone, we can read your Facebook messages or your text messages," said Drake. "We can read your call logs to see who you've been calling and spread the attack to those people."0

One of the most common ways to hack people is through text messages that appear to come from retailers or legitimate businesses.

"'You just won a free trip to Hawaii, to claim your trip or to unsubscribe, click on the following link' -- I don't want this."

So I unsubscribe. An innocent mistake that takes me deep into the belly of a cyber attack.

"The link is malicious," said Avraham.

And that's how they hacked me, by trapping me. Unsubscribing or accepting the prize offer in this text takes me to the same malicious site.

"Either way: Unsubscribe or win the trip, you lose," said Avraham.

What I should have done is hit "delete," because now the hackers have gained control of my phone from that one text.

Over the course of two days, they've downloaded my personal photos, and they have been tracking my exact location using the phone's GPS.

But they can also hear and record my conversations -- all my conversations, on the phone and in person.

I meet my friend at a coffee shop. I set my phone on my purse. It's in "sleep" mode, the screen is dark. While Paula and I are chatting inside, the hackers are outside, eavesdropping on the entire conversation. Drake and Avraham have turned on the phone's microphone and the camera. They can hear everything and they can see me. It's like I'm bugged.

But how would i know? My phone screen is dark. Not only am I oblivious, but people walking by the hackers have no idea what they're up to. It looks like day at the office for the tech crowd in San Francisco.

"Protecting smartphones is a difficult thing," said Avraham.

They hacked me with a malicious text message, but it there are so many other ways they can target you. Hackers can get to you through an email, Facebook messenger or one of the many chat apps.

But the worst way they get you is through a text message so stealth, you don't have to do a thing, and deleting it won't work either.

And if you think this couldn't happen to you, think again.

"We estimate 1 billion Android devices are vulnerable today," said Drake.

While this specific vulnerability was found on Android phones, the hackers say iPhones can have problems too.

"I think personally that Android phones and iPhones are on a level playing field when it comes to security," said Drake.

Since Zimperium discovered the security flaw in Androids, they also designed the patch to fix it, which is available now for free. It's simple: All you have to do is go into your settings and update your phone's software.

"If you didn't get an update in the past three months, you can throw away your phone, if you care about security," said Avraham.

So that phone you can't live without, that makes your life so easy, could become "public enemy number one" if you're not careful.