...Called XSS fragmentation, the vulnerability consists of multiple chunks, or fragments, of JavaScript malware that can slip by a filter or firewall because individually they don't constitute a security risk. But when they are combined after hitting the site, they can then be dangerous.

XSS fragmentation is rare, but a potentially powerful vulnerability that could be used against community-based sites such as MySpace or Web-based mail systems...MySpace in particular is vulnerable because it takes user-supplied content and stores it without adequate filtering...