A recent surge in hacked iTunes accounts has set off a wave of concern among Apple customers. According to technology blog The Next Web, "a number" of iTunes App Store users have reported that their accounts were hacked and then used to fraudulently purchase hundreds of dollars worth of applications. But some say the problem is relatively isolated. Here, a quick guide:

What happened?
On Sunday, two iPhone app developers noticed that 41 of the top 50 best-selling books on iTunes came from a single app publisher, Thuat Nguyen and his company called "My Company." Meanwhile, users began to report that their iTunes accounts had apparently been hacked and used to purchase Nguyen's apps, which explained the suspicious boost in sales. Further investigation showed that other developers were also defrauding customers for hundreds of dollars.

How many fraudulent developers are involved?
In addition to Nguyen — whose e-book apps have all since been removed from the App Store by Apple — at least four other developers have been identified as alleged scammers.

How much money have they stolen?
While the total amount has not yet been reported, afflicted customers were illegally charged between $100 and $1,400 each. Some users were charged up to $600 for a single application.

How serious is the problem?
The compromised accounts belong to customers "from across the globe, not just the U.S.," reports blogger Zee in The Next Web. That said, "the actual number of accounts involved are minuscule compared to the 100 million active iTunes accounts," says Arnold Kim in MacRumors. So while "the issue of hacked or compromised iTunes accounts is a major issue," it's no time to panic.

How do I know if my account has been hacked?
First, check you previous purchases in your iTunes account, as well as the bank account or credit card attached to your iTunes account. If you notice any purchases you did not make, contact Apple and your bank immediately.

How do I keep my account secure in the first place?
Regularly changing your iTunes password adds a greater level of protection against swindlers. The safest, if not particularly practical, approach, say insiders, is to make all your iTunes and App Store purchases using only iTunes gift cards, which limits the amount that can be lost in a scam.

Sources: The Next Web (2), Telegraph, Engadget, MacRumors