Actress Jennifer Lawrence is among the celebrities who made unwanted headlines when hackers leaked their personal photos onto the Internet.
But it turns out - your private pictures and information could fall into the wrong hands just as easily.
The Internet makes it easier than ever to make a few bucks, by selling your old smartphone.
But Tommy Nikolai and his family discovered the transaction could leave you vulnerable.
Local news from across Southern California
Nikolai posted his iPhone4 on eBay, taking care to wipe it clean before sending it to the new owner.
"I did a full factory reset and it still somehow accessed my password and information," Nikolai said.
He said the buyer, apparently unhappy with the purchase, managed to hack into his system, changing the passwords on his new iPhone and his Apple laptop.
"It's crazy," he said. "Within a few days everything that I had was in lock mode and I couldn't get into it."
Then the laptop prompted him to enter a pin code he never set and an eerie message appeared: "You deceived me and sold iPhone4."
"I need that guy's email and his password that he set on my phone to unlock it," Nikolai said.
According to an Apple spokesman, the buyer had accessed Nikolai's iCloud, and used the "find my phone" app to declare his phone and laptop as stolen, so he could no longer use them.
Computer science professor Jonathan Voras said it's possible that password information was left behind, making it possible for the buyer to seize control of Nikolai's devices.
"Technology that makes it easier for us to access it could potentially make it easier for us to access it as well," Voras said.
iPhones aren't the only vulnerable devices.
In 2014, security researchers purchased 20 used Android smartphones on eBay - and within hours were able to collect 40,000 stored photos - more than 750 emails and text messages - and one completed loan application.
Apple eventually let Nikolai unlock his phone and laptop - and set up a new iCloud password.
But from now on, he and his family plan to be more careful.
Apple said Nikolai neglected one important step when he sold his phone.
Before restoring an iPhone to factory settings, you have to logout of your iCloud account.