You want to make sure that appropriate files and directories are chmod-ed/permissions for those are appropriate. For all directories you want
find /opt/lampp/htdocs -type d -exec chmod 711 {} \;
And for all the images, JavaScript, CSS, HTML...well, you shouldn't execute them. So use
chmod 644 img/* js/* html/*
But for all the logic code (for instance PHP code), you should set permissions such that the user can't see that code:
chmod 600 file