Installation security hints/64/en

From LimeSurvey Manual

SSL usage

We generally recommend the usage of SSL for sensitive survey data. You usually enable SSL by configuring your web server correctly and using a SSQL certificate. If you have enabled SSL, you should enforce SSL all the time from the global settings of LimeSurvey. Additionally, you could only set to use 'secure' cookies by editing the respective option in config.php.