In the early 1990s, the Internet was young and Kevin Mitnick had the run of PacBell.

In his autobiography, "Ghost in the Wires," the one-time hacker -- and current security consultant -- tells how he convinced telco engineers to divulge technical details of their systems and set up custom circuits and wiretaps. Using social engineering and a few vulnerabilities, Mitnick -- throughout his 20s and early 30s -- had little trouble bending the system to suit his needs, whether grabbing the source code for the flagship products from DEC, Nokia and Sun or creating false identities.

For companies, the details behind the hacks and scams hold a lesson. While technical adeptness proved critical for Mitnick in some cases, it was the hacker's ability to talk the lingo and find ways around security policies that served him best. For companies who want to protect their intellectual property, the lesson is that social engineering is the danger and a good security policy the defense.

"Social engineering is using deception, influence and manipulation to get a target to comply with a request," Mitnick now says. "Back then, it was usually to release information that would be valuable to get into the company; nowadays, it is to get a person to do an action item -- go ahead and open up this JPEG, for example."

In one episode early in his tale, Mitnick aimed to get access to a feature of PacBell's infrastructure know as the Switched Access Services, or SAS, unit. The large refrigerator-sized box was used for testing the telephone lines, but could also be used to connect to any phone line and listen to a call in progress.

Mitnick tracked down the product to a company that had gone out of business. Finding the names of former employees, the hacker called one and asked for information on who currently could help with SAS. Using the name of the former employee and donning the persona of a real PacBell engineer, Mitnick convinced his target to send him critical data on how SAS operated and the key to his ability to wiretap any PacBell customer.

Difficult? Not really.

"Even thought I had been practicing the art of social engineering for years, I couldn't help but be amazed and a little dazzled by how easy this had been," he wrote in "Ghost in the Wires," coauthored with William Simon.

Social engineering has become a key component of most attacks. Spammers frequently grab the week's most popular headlines and news topics to attract end users to click on e-mailed links; phishers attempt to create Web sites that look like the real thing; and, online thieves use social networks and other reconnaissance techniques to profile the best victims within a targeted business.

While vulnerabilities in code have become harder to exploit, vulnerabilities in human behavior are often easy to abuse. Moreover, exploiting people typically allows more direct access into a company's systems, says Mitnick.

"These days, you see a lot of SQL injection, web-app problems, but that typically only gets you into a DMZ," he says. "Social engineering frequently gets you directly into the internal network."

In many ways, the differences between the early 1990s and the state of online security today is merely a measure of degrees and different technologies. In the past, Mitnick would fool people by having them call a company number that then routed to a line he controlled. Today, attackers do similar techniques using the domain name system or, in less sophisticated cases, using long URLs that appear like a familiar name.

"Yesterday, it was call forwarding; today, it's about DNS," he says.