They seem to do the following according to their FAQ[1]:
- "We utilize the latest encryption technologies, including a feature known as Perfect Forward Secrecy which goes a step further than traditional SSL by using a unique public key for each individual session"
- "Even server logs are disabled to ensure that any identifiable information your browser may be broadcasting" with requests are never read or stored on our servers.
- "On top of all that we utilize an extra layer of query encryption at the client side in order to ensure that your history remains private from other users who may access your computer"