There was a critical Java patch released yesterday: FP-Updater Tool addressing this bug: CVE-2010-4476 Released.
The bug was around Java inability to parse the following double numbers : 2.2250738585072012e-308 or 2.2250738585072011e-308 - parsing these numbers will result in Java thread hanging indefinitely.
This bug unfortunately affects ColdFusion sites as well, below are two useful blog posts that I found: