Apple fixes two security risks and improves compatibility in an update provided to Safari 4.0 users today. The update, which weighs in at 40MBs for Leopard users "improves the stability of the Nitro JavaScript engine and includes the latest compatibility and security fixes." 

The security update portion of Safari 4.0.2 will fix two security risks, one of which could allow an attacker to use cross-site scripting on maliciously coded sites. You can read more about the security update on the Apple knowledge base.

Apple is recommending this update to all Safari 4.0 users, and because of the security fixes, we would recommend it as well. You can download the update by opening Software Update on your Mac (Apple menu > Software Update), or by visiting the Apple Support Downloads website and downloading the installer package.