Why Windows blocks the installation of certain files

To help protect your computer from potentially harmful files, Windows XP Service Pack 2 (SP2) sometimes prevents you from installing files over the Internet Documents requested or received. This can occur if the file contains an ActiveX control or Web browser add-on that does not have a valid digital signature.

What are ActiveX controls and Web browser add-ons?

ActiveX controls and Web browser add-ons are small programs that are widely used on the Internet. They can make browsing more fun by providing toolbars, stock tickers, videos, animated content, and more. However, these programs may cause problems or provide you with unwanted content. In some cases, these programs can be used to collect information from your computer in ways you do not allow, corrupt data on your computer, install software on your computer without your consent, or allow others to remotely Take control of your computer. Because of these risks, you should install an ActiveX control or add-in only if you fully trust the publisher.

What is a digital signature, and what does a digital signature tell me about a file?

A digital signature is a way of electronically marking a document with information. At this point, the file will be signed by the creator (publisher). A valid digital signature will tell you two things about the file: the name of the publisher, and that the file has not been altered since it was signed. Any tampering will invalidate the signature.

If the file signature is invalid or the information in the digital signature looks suspicious, do not open the file. This will help avoid situations where someone might publish files that don't belong on the site, or add harmful content to files that don't belong to them.

Remember, a digital signature does not guarantee that the file is harmless. Signed files may still contain harmful code if the file was created in this harmful way. This is why when you start opening certain file types from email, Windows will ask you if you want to open the file, even if it has a valid digital signature.

For information about digital signatures and how they help you decide which files to open or install, click Related Topics.

Key Points

The default security settings in Internet Explorer are designed to help protect your computer from Internet viruses and attacks. Microsoft strongly recommends that you keep these security settings at their default levels or higher.

Change the default security settings in Internet Explorer

Open IE --> Tools --> Internet Options --> Security --> Custom Level --> Reset to: Security level - medium (or medium-low) --> Reset --> OK

Flash cannot be played because the latest Flash player is not installed, such as: Adobe Flash Player 9 ActiveX

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