When you transfer a file to your computer, you're downloading it. Downloading includes installing programs from a CD, opening pictures or links to Web sites from e-mail, copying Microsoft Office Word documents and Microsoft Office Excel spreadsheets from the company network, upgrading software acquired from the Web, or transferring music files from a computer half a world away. These files could be exactly what they say they are—but they can also be a vehicle for something with malevolent intent. Malware (malicious software) is software that can harm you or your computer; this category includes viruses, worms, spyware, and other destructive programs. Releasing a virus can destroy data or give someone access to all the information on your PC. And this can have a disastrous impact on your company, particularly if the virus destroys proprietary information such as mailing lists or other confidential information. Another potential threat is spyware. The most common forms of spyware often change your computer's behavior—like slowing it to a crawl or even causing it to crash. Even more alarming, spyware can be used to track your browsing habits, steal passwords, and even allow an attacker to gain control of your system. Malicious software can be installed on your computer without your knowledge or explicit consent, or it can be bundled with a program you intended to download. For example, you might think you are downloading a game, only to find out that the "game" found your credit card number on your computer and sent it to an attacker. Some malware spreads itself by sending e-mail from an infected computer to every e-mail address it finds.
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