Security Tip (ST04-012)
Browsing Safely: Understanding Active Content and Cookies
Many people browse the Internet without much thought to what is happening behind the scenes. Active content and cookies are common elements that may pose hidden risks when viewed in a browser or email client.
What is active content?
To increase functionality or add design embellishments, web sites often rely on scripts that execute programs within the web browser. This active content can be used to create "splash pages" or options like drop-down menus. Unfortunately, these scripts are often a way for attackers to download or execute malicious code on a user's computer.
What are cookies?
When you browse the Internet, information about your computer may be collected and stored. This information might be general information about your computer (such as IP address, the domain you used to connect (e.g., .edu, .com, .net), and the type of browser you used). It might also be more specific information about your browsing habits (such as the last time you visited a particular web site or your personal preferences for viewing that site).
Cookies can be saved for varying lengths of time:
- Session cookies - Session cookies store information only as long as you're using the browser; once you close the browser, the information is erased. The primary purpose of session cookies is to help with navigation, such as by indicating whether or not you've already visited a particular page and retaining information about your preferences once you've visited a page.
- Persistent cookies - Persistent cookies are stored on your computer so that your personal preferences can be retained. In most browsers, you can adjust the length of time that persistent cookies are stored. It is because of these cookies that your email address appears by default when you open your Yahoo! or Hotmail email account, or your personalized home page appears when you visit your favorite online merchant. If an attacker gains access to your computer, he or she may be able to gather personal information about you through these files.
To increase your level of security, consider adjusting your privacy and security settings to block or limit cookies in your web browser (see Evaluating Your Web Browser's Security Settings for more information). To make sure that other sites are not collecting personal information about you without your knowledge, choose to only allow cookies for the web site you are visiting; block or limit cookies from a third-party. If you are using a public computer, you should make sure that cookies are disabled to prevent other people from accessing or using your personal information.