Antivirus software company Symantec signed an agreement to buy Platform Logic, a maker of intrusion detection software (IDS) for an undisclosed sum, according to information obtained by IDG News Service.

The deal, which was disclosed Friday, will add Platform Logic's AppFire host intrusion prevention software to Symantec's stable of security technology, and gives Symantec new technology for blocking unknown, or "zero day" exploits, Trojan horse programs and spyware, according to a Symantec e-mail message announcing the deal.

A Symantec spokeswoman confirmed that an agreement was signed to acquire Platform Logic. However, the company could not share details about the acquisition until "the deal closes," according to spokeswoman Linda Smith Munyan.

Symantec expects its deal with Platform Logic to close "soon," Smith Munyan said.

Platform Logic did not respond to requests for comment.

Platform Logic was founded in 2002 and makes software that uses behavioral detection to protect individual computers, or hosts, from threats. In contrast to traditional antivirus software that relies on so-called "signatures" derived from samples of new viruses and worms, Platform Logic's AppFire looks for software application and operating system behaviors that are abnormal, and blocks those, according to the company's Web page.

The company's AppFire Suite Version 3, which was released in March, runs on servers and client computers running Microsoft's Windows, Sun Microsystems's Solaris and Red Hat's Linux operating systems.

For example AppFire can intercept a virus' or worm's hijack instructions before they are executed by comparing them to a set of typical instructions used by the targeted software application, according to the company's Web page.

Symantec already markets and sells host IDS technology, but said that the Platform Logic technology is complementary to what it now has and provides new capabilities for behavior analysis and blocking, application-specific protection and protection against spyware and eavesdropping programs, according to the e-mail message.

The addition of the software will reduce the time needed to protect systems from new threats, and will reduce the need to immediately deploy critical software patches. Symantec plans to integrate AppFire's technology into "an integrated server security solution" with antivirus, behavioral analysis and blocking and other host-based threat prevention technologies, the e-mail said.

The acquisition of Platform Logic is more evidence that the antivirus software market is evolving, and that traditional signature-based protection is on the wane, according to Pete Lindstrom of Spire Security.

Technology like host intrusion prevention is the "future" of antivirus software, as antivirus vendors look for ways to stop reacting to new threats and, instead, spot and prevent threats based on an understanding of what is legitimate and illegitimate behavior, he said.