An XSS (cross server scripting) security risk has been identified that affects all versions of JEvents since 1.5.0.
You should upgrade to the latest version of JEvents as soon as possible.
The latest version at the time of writing is 2.0.11.
Club member preview version 2.1.4 also includes this fix.
If you are continuing to use version 1.5.5 for some reason then version 1.5.6 is available from http://joomlacode.org/gf/project/jevent ... e_id=16213.