See reportings in http://forum.piwik.org/read.php?2,78979
When clicking on Security Tab in Settings Fatal error: Class 'Piwik_Http' not found in /home/piwik/public_html/plugins/SecurityInfo/PhpSecInfo/Test/Application/php.php on line 34
The class 'Piwik_Http' that class 'PhpSecInfo_Test_Application_Php' is trying to use doesnt appear to be loaded.
By adding class 'Piwik_Http' to '/plugins/SecurityInfo/PhpSecInfo/Test/Application/php.php' allows the method 'PhpSecInfo_Test_Application_Php' to use the class and then the Security Page page works.
Adding the following code before trying to use the class fixes the issue as a temporary solution:
if (!class_exists('Piwik_Http', false))
I think some sort of check for dependent classes should be introduced and should fail during automated tests.
PHP 5.3 Piwik 1.5.1
Keywords: class extends doesnt exist
please create only one bug for all these, also they are invalid, see Anthon note: http://forum.piwik.org/read.php?2,78979,page=1#msg-79034