We have fixed a Cross-Site-Scripting (XSS) vulnerability with that it was possible to create a link that will execute Javascript within the Admidio page.
We recommend you to read our announcements for version 4.0 if you have not done before.
If you are new to Admidio and want to install it on your webpage than the following wikipage could help: Install Admidio
The following wiki pages maybe interesting on an Update: Update Admidio