In an internal code review, Juniper has tracked malicious code that makes its Juniper and netscreen appliances accessible from the outside and can listen to VPN connections. Juniper advise you to install the patch immediately.

We advise all customers with appropriate Juniper systems for the current import of the current ScreenOS Update v6.3r21. If you have any questions or need help, please contact our support team.

More info: http://forums.juniper.net/t5/Security-Incident-Response/Important-Announcement-about-ScreenOS/ba-p/285554