Is it it normal for a full scan to take so long?

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...see How an Anti-virus Program Works.
• Options to scan for rootkits, adware, riskware and potentially unwanted programs (PUPS).
• 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).

To speed up a scan, clean out temporary (junk) files first, 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. You can also speed up a scan by using file exclusions...What Files Should You Exclude?.

In most cases when performing routine security checks, only a Quick Scan is needed since it checks the areas of your computer most likely to contain malware...the most prevalent and common places where malware typically hides. A Full Scan is much more comprehensive and can take a long time since it checks the entire hard drive (all folders/files) which can number in the thousands. The length of time for performing this type of scan varies because it is so comprehensive and therefore can take several hours. As such, a Full scan is generally recommended only for heavily infected systems...showing obvious indications (signs of infection and malware symptoms) that something is wrong.