If you are a Website Optimizer issue, you should immediately update the code on your website with the new one provided by Google. Google has fixed a Cross-Site Scripting (XSS) bug in their control script which can allow an attacker to execute malicious code on your site.
However, according to Google this attack is only possible if your website or browser has been compromised by a separate attack. Google has sent out notes to all users about the issue with instructions on how to update your code. Make sure to do the changes immediately.
Website Optimizer is a part of Google Analytics, however, no other services in Analytics seem to have been affected by this.