Files you download might be just what you expect, but they might also be a vehicle for malevolent intent. Malicious software (also called malware) is software that can harm you or your computer. Malware can contain viruses, worms, spyware, and other unwanted programs. Before you download files, make sure you are as protected from unwanted software as you can be.

Keep your software up-to-date

Update Windows automatically. If you use Windows Vista, Windows XP, Windows 2000 Service Pack 3(SP3) or later, or Windows Millennium Edition (Me), Automatic Updates delivers updates to your computer automatically, which is the easiest and most reliable way to make sure that you get new security and other high-priority updates as soon as they become available. To turn on Automatic Updates, visit Microsoft Update.

If you use Windows 2000 SP2 or earlier, Windows 98, Windows 95, or Windows NT Workstation 4, you can go to Windows Update for the latest security updates. (Make sure to return regularly.)
Use antivirus and antispyware software and regularly download the latest updates. Use security software such as Microsoft Security Essentials to help protect your PC. Microsoft Security Essentials is a no-cost download that works in the background to help stop spyware and virus intrusions. Microsoft Security Essentials is available for Windows XP SP2 and higher, Windows Vista, and Windows 7.

Improve your computer's overall security

Lay the protective groundwork. Use a firewall, keep your operating system updated with the latest security updates, and use both antivirus and antispyware programs. Learn more about how to better protect your computer.
Set your antivirus program to scan all incoming files and e-mail attachments before you open them. This is done differently in every antivirus program, so consult the manual or online Help for instructions.
Use a spam filter. Many e-mail programs offer filters that can help block unwanted messages. Microsoft Outlook has strong natural defenses against junk e-mail, but you can also step up your defense against spam.
Install and run a program to help detect and remove spyware. Some Internet Service Providers (ISPs) include antispyware software as part of their service. If your ISP (Internet service provider) doesn't offer this, consider Microsoft Security Essentials or Windows Defender. Microsoft Security Essentials is a no-cost download available for Windows XP SP2 or higher, Windows Vista, and Windows 7. Windows Defender comes with Windows Vista. If you use Windows XP SP2 or higher, you can download Windows Defender for no charge.

What to know about a file before you download it

Pause before you open attachments and click links
- Never open e-mail attachments or instant messages from strangers. If you know the sender, but the message arouses your suspicions, check with the sender before you open the attachment. If they did not send it, delete the e-mail message and ignore the instant message.
- Think twice before you click links in e- messages or instant messages. (If you know the sender, check before you click.) The same goes for pop-up windows and banner ads. Be especially wary of clicking links that accompany a request for confidential information-such as ones that say "Click here."
- Do not click "Agree," "OK," or "I Accept" to get rid of pop-up advertisements, unexpected warnings, or even offers to remove spyware. Instead, close the window by clicking in the upper-right corner, or by pressing ALT+F4 on your keyboard.
Download from reputable sites
Be cautious about downloading from Web sites if you were referred there by e-mail messages from unknown sources. Also be wary if sites contain objectionable material, make offers that seem too good to be true, or that do not include a clearly written privacy statement.
Respect the law
Remember that the words, music, software, games, or video files you download are someone's original work. You (or your kids) risk serious legal trouble if you use copyrighted material without the permission of its rightful owner. Violating the federal laws that govern the use of this material can lead to fines and even jail time. Note, too, that there are some files, such as certain kinds of pornography, that are illegal to intentionally download, view, or own.
Install and use file-sharing programs cautiously
When you use file-sharing (also known as peer-to-peer or P2P) programs to trade music, video, and other files on the Web, you make some of your files available to others using similar software. Using some file-sharing programs can also make your computer vulnerable while it's connected to the Internet.

File-sharing programs present other risks. They can be purveyors of malware. Or they might lead you to download something that is illegal, such as copyrighted songs or certain kinds of pornography. After some of these programs are on your computer, they can be tough to remove.