This is a very important update to apply to your sites as soon as possible because it fixes a security bug. We would rate this update as "critical".
This issue affects all versions of SiMan CMS 1.6.X, so if you are still on a elder releases you need to update to 1.6.4 as well.
Please upload the file http://simancms.org/files/download/security-update-20130916.zip via "Upload package" section of your Control panel.