An internet thief or internet scammer is someone trying to take something from you like your money or your personal information. Scammers usually asked for things like social security number and credit card number. A way they do this is by talking to you(usually on the phone) tells you that he or she can get you so much money by doing something, people usually want more money so some people who aren't careful say yes and give the person information.
A way you can protect yourself from being scammed is never give away personal information online to someone you don't know. This sounds easy enough but people who really need the extra cash don't think twice about what they do. Another way to protect yourself is never tell anyone your passwords and if you do tell someone, then change your password.
A very popular scam is people saying that they are someone who has a lot of power and money. Most of these people say that they are from another country and that they need your money to buy a plane ticket to meet them. An easy way to stop this is by not giving anyone money if you don't know them in person.
Another thing that are scams/viruses are pop up things that say they will protect your computer or make it run faster. Never trust these because they ask for information that is important like your credit card number.
Citizens Advice says that there are almost four million people scammed each year. That number is surprising because that's a lot of people who fall for tricks and people asking for information. You could avoid being one of these people by not giving away ANY personal information online.
To put this number in perspective, its about as much people as people who went to World Youth day in 2013.