As nude photos of more than 100 celebrities began circulating the internet this week, the spotlight turned to Apple and its popular iCloud service, believed to be where the hacker obtained the photos. Apple is just one of many companies that uses — and offers users access to — the cloud. But what exactly is the cloud?

Shortly after explicit photos of Mary Elizabeth Winstead — and 100 other celebrities — began circulating on the Internet this week, she took to Twitter, saying: “Knowing those photos were deleted long ago, I can only imagine the creepy effort that went into this.” Winstead might have deleted her copy of the photo long ago, but what she didn’t do — or perhaps even couldn’t do — was delete Apple’s.

Knowing those photos were deleted long ago, I can only imagine the creepy effort that went into this. Feeling for everyone who got hacked.

"It’s not that it’s impossible to delete things," said Corynne McSherry, intellectual property director at the Electronic Frontier Foundation. "It’s just that realistically, in our brave new world, it’s very difficult to be absolutely positive that something you’ve deleted, that there is no copy anywhere."

Such is life in the cloud.

Winstead — like millions of other iPhone users — was keeping photos in Apple’s iCloud. And as Ken Leeser, president of Kaliber Data Security, explains, whether you realize it or not, your life, too, is in the cloud.

"The way that the majority of people use technology today is cloud based, whether it's Uber or Fitbit or Facebook or Twitter," Leeser said.

So what exactly is the cloud? The term has become ubiquitous since 2006, when Eric Schmidt from Google called cloud computing the “emergent new model.”

"So what cloud computing is, is a way to have a central repository of information,” Leeser said. "Sometimes that information is manipulated at the data-center level, but then it’s returned back to the device, whether it's PC, a laptop, or a smartphone, or tablet."

What that means is that fewer digital things — whether it's your photos, emails or credit card transactions — are stored exclusively on your device. Increasingly, they are also on somebody else’s.

"People talk about the cloud and it’s like magic or something, but of course its not," McSherry said. "What you are doing, as a practical matter, is you are giving a third party a copy of your content. Your photo, your data, whatever — you are giving them a copy."

Now there isn’t just one cloud. When you and your colleagues work on a shared Google Doc, that stays in Google’s cloud. When you share a photo on Instagram, a copy lives in Instagram’s cloud. To further complicate matters, Instagram, like Netflix, Airbnb — and even the CIA — rents their cloud space from

"What happens to that copy is governed in part by a contract which no one reads, of course," McSherry said. "And then there’s the practical part, which is once you give a third party control over your information, then you’re vulnerable if that third party doesn’t carefully protect your data. There is nothing really you can do about that as a practical matter."

Despite hacker attacks this week on Apple and Home Depot, Lesser says that protecting your data is something cloud services generally do well, often better than small companies or individuals could do themselves.

"I guess it's the difference between whether or not you put your jewelry in a safe deposit box or keep it in a pouch in a cookie jar in a kitchen," Lesser said.

But both McSherry and Jeff Flowers, CEO of data storage software company Storiant, point out that security is not the only reason to be vigilant about what information you release into the cloud.

"All these services that are free — they are not free, you’re just not paying for them in money, but your paying for them in information," McSherry said. "That’s the bargain that you’re striking."

"For example, Google email and Facebook, we’re in new territory because those organizations look through your private communications and your pictures to try to glean advertising information from you," Lesser added.

There are things you can do to protect your privacy, from changing your passwords regularly to paying a little extra for services that offer you more control over your data. But Flowers points out that, these days, if you want to stay connected to the world, you simply can’t avoid the cloud.

"We're moving forward, this technology is here to stay and we just have to figure out how we're going to deal with it," he said. "There's no doubt we'll have great conveniences, and with any great convenience comes great concerns."

Sounds like a partly sunny/partly cloudy forecast for the future to me.