CERT/CC Malicious Web Scripts FAQ - A problem has recently been identified that can be found on a wide variety of web sites: what you receive from a web site may not be what that site meant to send. If you click on a specially designed link, the site may unknowingly send you bad data, unwanted pictures, and programs (malicious scripts) to compromise your data. The problem is not with web browsers themselves but with how web pages are constructed and how data entering and leaving web sites is validated. "Validate" means ensuring no "unintended" characters are sent back to the client.
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