There are numerous reports that JailbreakMe 2.0 has been released with support for iOS 4. All that's needed to jailbreak an iPhone, iPod or iPad is to visit http://www.jailbreakme.com and then to engage the drive-by script.
We're currently investigating to learn more about the vulnerability being used… if the vulnerability can be used to jailbreak, it can also be used for more malicious drive-by exploits. (JailbreakMe's website has been online since late 2007 and they appear to be legitimate enthusiasts.)
And on the topic of iOS vulnerabilities, we've updated the spreadsheet linked in last Friday's post to include a category list and chart.
WebKit and Safari account for 64% of iOS's security fixes.