Hacker
The term hacker was once used to illustrate a clever programmer. Today, it’s applied to those who exploit security vulnerabilities to break into a workstation system. You can think of it as electronic burglary. Hackers regularly break into both character computers and large networks. Once they have access, they may install wicked programs, steal confidential data, or conceivably use compromised computers to share out spam.
Hackers are like electronic burglars, who use loopholes in your programs - vulnerabilities - to break into your computer system. You can protect yourself from hackers by using a firewall. A firewall program, which often comes as part of an anti-virus software package, protects a PC by detecting potential intruders and making the PC invisible to hackers.

Exposure
Today’s computer software is very complex, comprised of thousands of lines of code. Since software is written by humans, it’s hardly unexpected that they contain programming mistakes, known as vulnerabilities. These loophole are used by hackers to break into systems; they are also used by authors of mean code to launch their programs automatically on your computer.