Apple has posted a security update for Safari Beta for Windows 3.0.4, the details of which are posted here.
WebKit allows a page to navigate the subframes of any other page. Visiting a maliciously crafted web page could trigger a cross-site scripting attack, which may lead to the disclosure of sensitive information. This update addresses the issue by implementing a stricter frame navigation policy. (This issue is addressed for Mac OS X in Security Update 2007-009.)
Apple released Safari Beta for Windows 3.0.4 in November.