US-CERT is aware of public reports indicating that attackers are using legitimate web pages to run malicious code on victims' machines.

Reports, including a posting by Sophos, indicate that these messages

• Include keywords and names related to the 9/11/2001 terrorist attack
• Prompt users with a fake virus scan that attempts to make users believe they have a security issue. The users are then asked to download fake security software that is actually malicious code.

• Install anti-virus software, and keep its virus signature file up to date
• Refer to the Avoiding Social Engineering and Phishing Attacks document for more information on social engineering attacks
  

Read more at: US-CERT Current Activity