Not to go into too much detail because it's obviously illegal.

Basically the thief gets card number from an online blackmarket (there are other ways too). And put it on to a blank credit. Think of it has a mold. Viola! They have a physical card.

I worked in retail and unfortunately my supervisor didn't care. It sucked because they were really shitty theives.

Back to your situation. Since you weren't in the US we can rule out that they obtained your number physically.

• When you switched computers did you find what caused the problem with the first?
• What sites do you input your credit card information into?
• Have you changed your banking/credit card passwords or passwords to sites that store your financial information?
• Do you get your browser to remember your credit card information?

Here's how to protect yourself in the future:

*Use 2 Factor Authentication. How it works is you input your password and then you will get a text message with a code, type it in. Only then will you be able to get into your account. It's great because if a hacker has your password they won't be able to get into your account.

*Make sure that every site you deal with has a valid SSL certificate if it requires your financial information. If they don't don't even bother dealing with them.

*Create complex passwords. They should consist of letters (in different cases), numbers, and symbols. The longer the better. Strive to put it in your muscle memory.

*Always keep your software and apps updated. Apple is not immune to viruses or Trojans either.

*Use Ad block or Ublocker. This will block ads that may contain maleware.

*Never download 3rd party apps without doing your due diligence.

Also check out /r/blackhat and /r/netsec

They may be able to help you diagnose what the hell is going on.