Antivirus programs are designed to detect and intercept harmful files downloaded to your computer. In order to monitor incoming files, however, antivirus programs--like all applications--need to use system resources. The degree to which an antivirus program detrimentally affects a system's performance varies from one application to another. CNET Labs tests three areas of antivirus application performance: how deep-file virus scanning impacts overall system performance, how quickly files can be scanned for viruses, and how system boot time is affected by the antivirus program. We also report on how effective the antivirus programs are at identifying viruses by citing the studies of established industry authorities.

Test environment

Antivirus software is tested on a desktop system with a 3.4GHz Pentium 4 550 processor, 1GB of DDR2 SDRAM running at 533MHz, an Nvidia GeForce 6600 PCI-Express graphics card with 256MB of memory, a 74GB Western Digital WD740 Raptor hard drive, and Windows XP Professional SP2 with the latest security updates installed. Once the antivirus software being tested is installed, we make sure the most recently available updates are installed, including the latest virus definitions. We test using the antivirus program's default settings.

System-performance impact test

Actively scanning a system for viruses can have an adverse affect on overall system performance, as the antivirus engine competes with other applications for system resources. When performing regular real-time scans, most of today's antivirus scan engines are sophisticated enough to relegate the additional overheard they introduce to the background and not significantly impact the performance of other applications. Performing deep scans, on the other hand, often requires enough of the available system resources for the antivirus engine to have a noticeable impact on the performance of other applications. Deep scanning is when the antivirus application scans every file located on all partitions found on each drive.

This set of tests is designed to measure how much performance degradation selected applications suffer when a deep scan is taking place. We first run the three tests listed below, before an antivirus application is installed. We then install the antivirus app and run the same tests again--this time while the antivirus program is performing a deep scan of the system.

iTunes MP3-encoding test
Using Apple's iTunes 6.0.1, we time how long it takes to convert 19 WAV files to 192Kbps MP3 files.

Sorenson Squeeze video-encoding test
Using Sorenson Squeeze 4.0.301.11, we time how long it takes to convert a 30-second DV AVI file to an MPEG-4 file.

Scanning speed test

Using the antivirus software being tested, we scan a 1.57GB folder of files that includes DLL, TXT, BMP, ZIP, WAV, and MIDI files ranging in size from 1KB to 8MB, and time how long this process takes to complete. The quicker it takes the antivirus program to scan the folder--relative to other antivirus applications--the more efficient the program is at scanning files.

Boot speed test

We time how long the system takes to boot from a full powered-off state until Windows starts and the antivirus software finishes loading. The quicker it takes the system to finish booting and loading the antivirus program--relative to other antivirus applications--the less impact the app has on boot time.

Effectiveness

Last, but certainly not least, we also consider how effective the antivirus program is at identifying viruses. Within each review, we comment on the historical findings of the virus-scanning engine from the extensive testing of numerous industry experts, such as AV-Comparatives.org and Checkvir.com.