In brief, a secure connection means that all data is encrypted (using RSA encryption) before being sent to you. This prevents any interloper ("sniffer") who might be watching you connect from seeing anything but fully encrypted data.
In order to use this feature, you will need to use the Netscape browser. This is available for free from Netscape Communications:
If you'd like to connect to us securely, we will honor all secure requests and return only secure links. Giving access this way enables us to provide full security while at the same time allowing for users who do not need or want it. What this implies is that the onus is on you to be aware of how you connect to us. If you choose the regular log-in procedure, we will not deny your access. However, we strongly suggest that you take advantage of the secure service. It requires no additional steps to accomodate it and the free browser from Netscape is an excellent product.
The one exception to this rule will be for brokerage services. The nature of this service requires that we enforce security to the fullest of our capabilities. All brokerage transactions take place under separate password protection and in a fully secure environment. The use of Netscape Navigator is required to take full advantage of our member brokers services.