NEW YORK — The circulation of nude photographs stolen from celebrities' online accounts has raised questions about the security of storing information over the Internet.
Apple Inc. acknowledged Tuesday that computer hackers broke into the accounts of several celebrities, a security breakdown Apple blamed on the intruders' ability to figure out passwords and bypass other safeguards.
Apple says it found no evidence of a widespread problem in its iCloud or Find my iPhone services. Instead, accounts were targeted by hackers who had enough information to know the user names, passwords, and answers to personal security questions, the company said.
The break-in has exposed weaknesses in online security at a time when more people are storing photos and other sensitive information on computers housed in massive data centers, a practice known as cloud computing.
Here is a look at how safe data are when stored remotely on these services.
Q. What is the cloud?
A. A way of storing photos, documents, e-mail, and other data on computers located elsewhere, so that you are not using space on your own computer, phone, or other device. Amazon, Apple, Google, and Microsoft offer cloud storage, as do smaller companies like Dropbox and Evernote.
The advantage is that you can access the same information from any device. And if you lose your phone, for example, you don't lose your vacation pictures. The drawback is that you are putting information somewhere else, so you run the risk of a hacking attack on those systems.
Q. Is it secure?
A. For the most part, yes. Companies invest a lot in trying to ensure that private information stays private.
''The short answer is the cloud is often more secure than other storage,'' says Rich Mogull, chief executive of the security firm Securosis. But that doesn't mean it is immune from attacks.
''Like a lot of Internet services, there are a lot of attackers who have a lot of time,'' Mogull says.
Q. How can individuals make their data more secure?
A. You need passwords to access your accounts, so choosing a strong one is important.
Tim Bajarin, an analyst at the technology research firm Creative Strategies, recommends different passwords for each account, so a breach in one won't compromise another. It is also important to have a number and punctuation mark in each password, or a creative spelling of a word to make it harder to guess. Avoid using common words or birthdays as passwords. A strong password is particularly important if you store sensitive information online.
Another way to make your information harder to hack is to use multifactor, or two-step, identification.
That means the first time you log onto an account from a new device, you are asked for a second form of identification. Usually, that involves getting sent a code as a text on your phone or in an e-mail.
''If you have physical possession of one of your other devices, the identification is really hard to break,'' Mogull says.
Most major cloud services offer this kind of protection. Amazon's Cloud Drive is the notable exception. But you usually have to turn this on.