SSL is a shorthand term for "Secure Sockets Layer" which is part of the TCP/IP protocol suite. SSL was developed by Netscape for use on their browser (Netscape Navigator) for transferring data over the Internet securley (eg, credit card details). SSL does this by using a public key to encrypt data.

Existing versions of IE automatically use the SSL 2.0 protocol. Microsoft have said that IE7 will support the Transport Layer Security protocol (TLS) by default. This is a stronger encryption protocol than SLL.