It’s cross-site scripting, or XSS, a violation of the same origin policy. XSS vulnerabilities occur when an attacker is able to cause a trusted Web site, such as an online banking website, to include a malicious script in the webpage presented to a victim. In that example, the script can then access the banking application with the privileges of the victim, potentially disclosing secret information or transferring money without the victim's authorization.
Finjan, a privately owned web security company, reported that the new toolkit is a very smart program and can easily avoid detection, adapt to new conditions and make an adjustment when patch released.
The user embeds malicious script into the websites himself. The script does not appear on the site after end-user’s first appearance. That’s why it’s almost impossible to track it down.
Though discovered the script is still active and harmful.