Bogofilter has released new security update on 09 July, 2010. This is the original security message from the Bogofilter developer:
The security update should be implemented as soon as possible, because in the older version, bogofilter could make, particulary, an email client software such as GNOME Evolution crashed.
You can use the patch for bogofilter 1.2.1 from the security annoucement or just upgrade your bogofilter to latest stable version, 1.2.2. The latest is the recommended method.