Just a little bit has been released version 2.6.3 of WordPress due to a failure found in Snoopy class, used in WordPress for displaying feeds on Dashboard. You can do the full update, or simply replace the affected file, and the file in which the WordPress version is stored.

WordPress 2.6.3 – 1.2MB (Download)

wp-includes/class-snoopy.php (Download)

wp-includes/version.php (Downloa(d)