Have you used a friend's laptop to charge your iPhone and gotten a prompt that says, "Trust This Computer?" Say yes, and the computer will be able to access your phone settings and data while they're connected. And while it doesn't feel like your answer really matters—your phone will charge either way—researchers from Symantec warn that this seemingly minor decision has much higher stakes than you'd think.

In fact, the Symantec team has found that hacks exploiting that misplaced "Trust" comprise a whole class of iOS attacks they call "trustjacking." Once a user authorizes a device, they open themselves to serious and persistent attacks while their phone is connected to the same Wi-Fi network as a hacker, or even remote attacks when the devices are separated.

Adi Sharabani, Symantec's senior vice president of modern operating system security, and Roy Iarchy, the modern operating system research team leader, will make that case Wednesday, in a presentation at the RSA security conference in San Francisco.

"Once this trust is established, everything is possible," Sharabani told WIRED last week. "It introduces a new vector of attack."

Sharabani and Iarchy's presentation focuses largely on a feature known as iTunes Wi-Fi Sync, the tool that lets iOS devices sync with desktop iTunes over Wi-Fi. For this process you physically connect a mobile device to a computer once, indicate that the iOS device can trust the computer going forward, and then enable iTunes Wi-Fi Sync from the PC. After that the two devices can sync and communicate whenever they are on the same Wi-Fi network without any further approval from the iPhone or iPad.

It's a reasonable and useful feature when used as intended. But an attacker could also plant a malicious computer—perhaps one shaped like a charging station or external battery—and trick people into connecting their devices and granting trust out of confusion or disinterest.

'Once this trust is established, everything is possible.' Adi Sharabani, Symantec

Once a trusted Wi-Fi Sync connection is established, attackers can not only do basic syncing, but also take advantage of controls meant for developers to manipulate the victim iOS device. A hacker could work quickly to install malware on the phone, or initiate a backup to gather data like a victim's photos, app information, and SMS/iMessage chats. Attackers with trust privileges could also start watching a target device's screen in real-time by initiating screenshots on the phone and then syncing them to the attack computer. Or they could play a long game, silently retaining their trusted status until it is long forgotten, for a future attack.

"We discovered this by mistake actually," Sharabani says. "Roy was doing research and he connected his own iPhone to his own computer to access it. But accidentally he realized that he was not actually connected to his own phone. He was connected to one of his team members’ phones who had connected their mobile device to Roy’s desktop a few weeks before. So Roy started to dig into what exactly he could do and find out if he were an attacker."

You can imagine a number of scenarios where this could work as a targeted attack. Everyone has places they visit regularly: an office, a coffee shop, the local library. Attackers could anticipate that a victim iOS device would regularly connect to the same Wi-Fi network as the trusted attacker computer—enabling clandestine, malicious backups with iTunes Wi-Fi Sync. The researchers point out that an attacker wouldn't necessarily be geographically limited; after gaining a foothold, they could combine trustjacking with a type of attack called "malicious profiles," which takes advantage of how iOS manages configuration packages for apps to get around access restrictions, establish continuous remote access. Beginning in iOS 10, though, Apple started making it harder for hackers to carry out malicious profile attacks.