The speed and ability to complete an anti-virus or anti-malware scan depends on a variety of factors.
- The program itself and how its scanning engine is designed to scan: using a signature database vs heuristic scanning or a combination of both.
- Options to scan for spyware, adware, riskware and potentially unwanted programs (PUPS)[/color][/url].
- Options to scan memory, boot sectors, registry and alternate data streams (ADS).
- Type of scan performed: Deep, Quick or Custom scanning.
- What action has to be performed when malware is detected.
- A computer's hard drive size.
- Disk size and used capacity (number of files that have to be scanned).
- Types of files (.exe, .dll, .sys, .cab, archived, compressed, packed, email, etc) that are scanned.
- Whether external drives are included in the scan.
- Competition for and utilization of system/CPU resources by the scanner.
- Other running processes and programs in the background.
- Whether the scanning engine stalls, hangs or freezes.
- Interference from malware.
- Interference from other security programs attempting to scan at the same time.
- Interference from other programs attempting to update (download/install) components from the Internet.
- Interference from the user (whether or not you use the computer during the scan).
For a more detailed explanation, read How an Antivirus Program Works.
-- Using two security scanning engines at the same time can cause each to interfere with the other, cause systems hangs, false detections, unreliable results and other unpredictable behavior.
-- Although they should not affect an anti-virus scan, if the screensaver, hibernation or Sleep Mode are not turned off before scanning, those features can sometimes have odd effects when attempting to perfom a scan. Some folks create special power schemes to use when doing their scans while others just turn these features off until the scan is complete.
* Learning Windows 7: Manage Power Settings
- Windows 7 Sleep and hibernation FAQs
* Power Options overview in Windows XP
-- It is not unusual for an anti-virus or anti-malware scanner to having problems with or be suspicious of compressed, archived, .cab, .rar, .jar, .iso, and packed files because they have difficulty reading what is inside them. These kind of files often trigger alerts by security software using heuristic detection because they are resistant to scanning (difficult to read). This resistance may also result in some scanners to stall (hang) on these particular types of files or just ignore (skip) them. Certain files in the System Volume Information Folder like the Tracking.log (created by the Distributed Link Tracking Service to store maintenance information) have also been reported as a source causing some scanners to hang.
To speed up a scan, uninstall unnecessary programs, clean out temporary files, temporarily disable any other real-time protection tools, close all open programs, perform a Quick Scan instead of a Full one and do not use the computer during the scan.