Contrary to what you may see in the movies, most hackers don't sit down in front of their computers and start trying to hack one individual computer. Rather, they write and release viruses onto the Internet to attack computers which come in contact with them. While products like Norton AntiVirus can protect you from many of the viruses and malware which hackers write, it cannot protect your computer from every digital threat.
How Anti-Virus Works
Software like Norton AntiVirus works by examining files and programs they find on your computer. This examination includes looking for patterns, or signatures, in the code that security researchers have identified as belonging to certain pieces of malware. It can also include executing the code in a protected environment, where a virus can't actually affect your computer, and seeing what it does. If the scan finds sufficient behaviors or codes which its databases associate with viruses, then the anti-virus software will flag the file and inform you of the threat.
Sneaking Past Anti-Virus
Hackers can try bypassing anti-virus scans altogether by attacking your computer through a different program. For example, hackers can embed malicious code in a video stream which will try to get the media player handling the stream to attack your computer. This malicious code tries to hijack the media player by exploiting internal security vulnerabilities. The fact that the media player is the program trying to attack your own computer hides the malicious code from detection by anti-virus scanners.
Even when a hacker doesn't try to attack your computer through a program you have approved to execute, he can still write malware which can potentially convince a virus scanner that it is not malware. Virus scanners look for certain signatures, so hackers get creative with how they write their code, so it won't match the signatures virus scanners use to evaluate files and programs. As anti-virus scanners update their signatures and methods, hackers adapt to try to stay one step ahead.
Not Perfect Protection
Norton AntiVirus does provide protection from hackers, but this protection is not perfect. Skilled hackers can find ways of evading its detection -- and can even try to trick you into installing and approving a virus that is disguised as a legitimate program. Even if you do get Norton AntiVirus, you need to protect yourself from hackers by avoiding questionable websites, streaming media from websites that you do not know to be reputable and only downloading software from sources which you trust.
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