We all know what it is. When you download unsafe document, game etc. you could get virus by those document. There are some types of viruses. One of them is not so hard to release. You can release those viruses with any kind of safe anti-virus program. And there is one type of virus too. It is hard to release form your computer and it may cause big problem such as information stealing. You can not release this virus with any kind of anti-virus program.
Spam is a threat that may disturb you a lot. It is so common thing. You receive emails from someone that you don't know. In those emails it says that "you won a prize!". When you click on that button your computer might get virus. It causes freezing more. But also it might capture your personal information. You can stop receiving those kind of emails by reporting the sender as a spam. It may protect you.
By using phishing, you could take people's personal information such as bank details. It may hack your any accounts by sending emails. You don't need to open it. If you've recieved that kind of email, it means that you've been hacked already.
As you can see, there are many ways to hack. And I didn't write all of them. Well, you can protect yourself if you behave wisely.