One of the main points DSL proponents tout as a benefit of DSL over cable Internet access is security.

Similarities
Both DSL and cable Internet access have more in common with a local network connection than a dial-up connection.

On a network connection, anything directed to a specific computer is broadcast over the entire network. This means that other computers in the same network as the intended computer will receive all the information sent to that one computer. Usually this isn't a problem because the other computers ignore anything not sent directly to them.

However, there are programs that allow those other computers to see the information intended for those other computers.

DSL
DSL works similar to the diagram below.

Data comes in from the Internet to your Internet Service Provider (or "ISP"), such as StarNet. The ISP is connected to US West's high-speed data network. It is this network through which all US West DSL users' data is carried.

The data intended for a DSL customer is sent to their nearest phone switch. From the phone switch, the data travels through your phone line.

This path is actually fairly secure. The data for all DSL users does get carried over the US West high-speed network, but only US West employees should have direct access to that data. Since the phone line running from the phone switch to your home isn't used by anyone else, no other DSL users can see the information intended for your computer.

Cable Modems
Cable modems work similar to the diagram below.

Data comes in from the Internet to the cable company's data network. The data is then sent on to a smaller network in a neighborhood (possibly a few blocks or larger). All the homes connected to that smaller network get all the information intended for the other homes in the area.

Again, this isn't a problem as far as using the service on a basic level. Your computer would ignore anything not sent directly to it. However, someone in the neighborhood could run a special program and see the information sent to everyone in the same area.