After the quick presetup scan, Norton installs itself, automatically downloads the latest virus definitions and program files, and runs a mandatory, comprehensive post-setup scan. Our initial setup took just less than 45 minutes; plan to step away from the PC and brew some tea in that time, though, as Norton is a major resource hog during its system scan, essentially rendering your PC useless for other tasks. For instance, in our informal tests, Microsoft Word took 35 seconds to load during a system scan. With no scan running, it took just 6 seconds on our 2GHz Celeron with 512MB of RAM. For more on system performance, see our performance results.

Norton's clean, well-organized interface remains one of the best in the antivirus biz, and we're pleased to see it's mostly unchanged. One noteworthy upgrade is the Protection Alert screen; it allows you to specify a period of inactivity when disabling Norton's real-time virus scanner--a necessary evil when installing some programs. Simply right-click the Norton icon in the Windows Taskbar, click Disable Auto-Protect, and select a period of shutdown time--15 minutes, 1 hour, 5 hours, or until the system restarts. This is important because many users forget to turn the scanner back on.
Like its competitors, Norton AntiVirus 2005 scans and cleans instant-messenger attachments, as well as inbound and outbound e-mail. However, all of Norton's best features are carryovers from 2004. This year's version adds Norton Internet Worm Protection, a lightweight firewall feature that blocks unsolicited inbound traffic, including nasty troublemakers such as the Blaster and Sasser worms. Unlike a full-on firewall, however, Worm Protection won't block outbound traffic, making it no more effective than the free Microsoft firewall included in Windows XP SP2.
We ran Norton Worm Protection against Steve Gibson's ShieldsUp security checker, which reported that our test PC successfully blocked most of the test Internet packets. Unfortunately, our test PC replied to the ShieldsUp Ping requests, meaning our computer was visible to the Internet--not good. Typically, a computer running a full-on firewall won't respond to pings. Even with Worm Protection, Norton users will still need a firewall.
Like its predecessor, Norton AntiVirus 2005 scans for hidden spyware threats, including adware, dialers, and keystroke loggers that record every key you tap. Unfortunately, its real-time scanner doesn't detect spyware; rather, Norton spots these menaces during only a full system scan or a Quick Scan, the latter of which runs immediately after virus-definition downloads. Overall scanning speed was respectable. In our informal tests, Norton took 37 minutes to scan a 12GB partition.
Version 2005's list price remains unchanged at $49.95 and is comparable to the cost of Trend Micro PC-cillin Internet Security 2004, which includes a full firewall and antispam tools not found in Norton AntiVirus 2005.
In CNET Labs tests, running Norton AntiVirus 2005 results in the same amount of drag on system performance as running McAfee and Trend Micro PC-cillin. The lightest hit on system resources comes from Computer Associates' EZ Antivirus. Norton took longer to scan our 1.3GB hard drive than either PC-cillin or EZ Antivirus.
