Is full system virus scan required when real time virus scan is enabled?

“I have a real time virus scan enabled. A full system virus scan consumes lot of my computer resources and time. So why should I run a full system virus scan regularly?”. This is a query which we come across frequently. This article tries to bring more clarity about full system virus scan and a real time virus scan.


Let me give my verdict upfront and then go about justifying the same. Going by the defense-in-depth principle, I will recommend that a real time virus scan should be complimented with a full system virus scan.


1. In most anti-virus softwares, real time scans are optimized for speed while the full system scans are optimized for thoroughness. Therefore, malwares can evade real time scans but get caught by full system scans.

2. There is a time lag between launch of a new virus and updation of virus signatures by your anti-virus software for that virus. If you receive a file infected with a boot sector virus during this time lag, your real time scanner will not find the virus (neither a full system scan will do that at that point in time). Now, your system is infected with the boot sector virus. In the case of a boot sector virus, virus will not be detected by the real time scanner as the system critical files boot up before the antivirus scanner every time you switch on your computer. So, even after your real time scanner is updated with the anti-virus solution for this boot sector virus, the boot sector virus will be missed out by the real time scanner. However, a weekly full system scan will capture the virus during your next weekly full system scan.

How to run a full system scan efficiently?

1. Schedule the full system scans during non-peak business hours / off-hours.
2. Delete unnecessary internet cache, temporary files and cookies.
3. If you still feel that full system scan is an overload on your computer resources, you may configure the full scheduled scan for a scan of all executable and system files.
4. You may schedule a full system scan once a week rather than daily.

5. Never give the end users the option to switch off the full system scan.

So next time when your anti-virus software is running a full system scan, don’t terminate it. It is working overtime to protect you!!

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