Zone Alarm makes several different types of software to protect computers from spyware, viruses, hackers and identity theft. Most require purchase, but Zone Alarm Firewall is free. Zone Alarm claims that their products are designed to be quiet and efficient and do not interfere with the normal operations of the computer.

On the Other: Yes, According to PC Spy

In 2006, the website PC Spy performed tests on several different kinds of security software, including Zone Alarm, Norton Internet Security Suite and McAfee Virus Scan. It ranked them according to how much time they added to boot time, how long they took to open by themselves and how much delay they added to file opening. Zone Alarm started quickly on its own but was one of the highest scorers in adding boot time and file delays.

Bottom Line

Any running program adds a drain on a computer's resources. Zone Alarm provides good protection with an easy-to-use interface. In the past, there have been issues with Zone Alarm adding file and boot delays; however, CNET reports that the free Zone Alarm 9.1.007, released in November 2009, "addresses specific stability and quality issues."

Source:

Zone Alarm: Force Field FAQ

PC Spy: What Really Slows Windows Down

CNET review: Zone Alarm 9.1.007