I found the problem. :)
My cpanel php variables manager puts a php.ini in every subdirectory (the server is set up so that php.ini settings do not apply to subdirectories).
Following a similar issue in this post [forum.piwik.org] it seems that phpsecinfo.php tries to read all files in /Test. I deleted the php.ini files in plugins/SecurityInfo/PhpSecInfo/Test and all subdirectories and that fixed it.
My cpanel php variables manager puts a php.ini in every subdirectory (the server is set up so that php.ini settings do not apply to subdirectories).
Following a similar issue in this post [forum.piwik.org] it seems that phpsecinfo.php tries to read all files in /Test. I deleted the php.ini files in plugins/SecurityInfo/PhpSecInfo/Test and all subdirectories and that fixed it.