Because it is significantly faster to connect via telnet to a system than to call the system with a modem, an attacker can try to guess more passwords in any given amount of time. Long distance calls cost the caller money, but there is usually no incremental charge for using telnet over the Internet. As a result, systems on the network are more subject to attack from around the country and around the world. It is often easier to access a system anonymously on the Internet than over phone lines. Modern telephone switching systems can trace calls in seconds and in many cases deliver the calling number to the system.
Internet protocols make it easier for an intruder to disguise the source of an attack.