Symantec is buy Platform Logic, a maker of intrusion detection software (IDS) for an undisclosed sum.

The deal 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.

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", it said.

Platform Logic was founded in 2002 and makes software that uses behavioural detection to protect individual computers, or hosts, from threats. In contrast to traditional anti-virus 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 behaviours that are abnormal, and blocks them.

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.

The company's AppFire Suite Version 3, released in March, runs on Windows, Solaris and Red Hat Linux servers and PCs.

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 behaviour analysis and blocking, application-specific protection and protection against spyware and eavesdropping programs.