How to run a full system scan on PC?

How to run a full system scan on PC: Steps

Performing a how to run a full system scan on PC is essential for maintaining computer security and identifying hidden threats across all storage drives. Understanding this procedure ensures you protect sensitive data effectively. Explore the necessary steps to initiate this comprehensive security check and maintain your device health.

How to run a full system scan on PC quickly and effectively

To run a full system scan on a PC using Windows Security, open the Start menu, type Windows Security, and go to Virus and threat protection. From there, select Scan options, choose Full scan, and click Scan now to begin the process. This may involve multiple factors depending on your hardware and software environment. But there is one counterintuitive factor that many users overlook which can make your scan take 5 times longer than necessary - I will reveal what that is in the scan speed section below.

Running a full scan is a deep dive into every file, folder, and running process on your storage drive. Unlike a quick scan, which only checks common hiding spots for malware, a full scan examines the entire disk for dormant threats.

I remember the first time I ran a full scan on my old laptop; I thought the machine had frozen because the progress bar did not move for twenty minutes. It turns out that modern security suites, including Microsoft Defender, achieve high malware detection rates. This high level of scrutiny is exactly why the process demands significant time and system resources. ^[1]

Step-by-step guide for Windows 10 and Windows 11

Performing a scan is relatively straightforward, but it is important to follow the correct path to ensure no partition is left unchecked. Most modern PCs come with Windows Security pre-installed, which serves as a powerful, built-in defense mechanism that requires no additional subscription fees.

Follow these steps to initiate the scan: 1. Click the Start button and type - Windows Security - into the search bar. 2. Open the app and select the Virus and threat protection icon from the left-hand sidebar or the main dashboard. 3. Locate and click on the Scan options link, which is usually found just below the Quick scan button. 4. Select the radio button for Full scan. This tells the system to check all files and running programs on your hard disk. 5. Click Scan now at the bottom of the page.

Once the scan begins, you will see a progress bar and an estimated time remaining. Do not be alarmed if the time fluctuates wildly. In my experience, the system often overestimates the time at the start and then speeds up once it moves past large compressed files. Let it run. If you are using a laptop, ensure it is plugged into a power source, as a full scan can drain a battery by 15-20% in a single hour due to high CPU usage.

Full Scan vs. Quick Scan: Why the difference matters

A common mistake is assuming a Quick Scan is all you ever need. It is not. Quick scans focus on folders like AppData and System32 where malware typically tries to launch itself during bootup. However, approximately 15-20% of sophisticated malware, such as Trojan horses or rootkits, can hide in deep directories or non-system partitions that a Quick Scan simply ignores.

Full scans are intensive. They can consume significant CPU power while active,^[2] which can lead to noticeable lag if you are trying to edit video or play games simultaneously. This is the trade-off for security. While a Quick Scan might finish in under 3 minutes, a Full Scan provides the peace of mind that comes from verifying the integrity of every single bit on your drive. Is it worth the wait? Absolutely. I usually schedule these for when I am stepping away for lunch or finishing my day.

Addressing the 4-hour wait: Factors affecting scan speed

If your scan feels like it is moving at the speed of a snail, there is likely a hardware or configuration reason behind it. Here is the counterintuitive factor I mentioned earlier: having multiple antivirus programs installed simultaneously. Many users think - more is better - but two real-time scanners will fight over every file, slowing the scan by up to 500% as they lock and unlock data repeatedly. Stick to one active shield.

Hardware plays a massive role as well. A traditional Hard Disk Drive (HDD) with 1TB of data can take a long time to complete a full scan because of the physical movement of the reading arm. In contrast, a modern Solid State Drive (SSD) of the same capacity can often finish much faster. This is because SSDs can access data almost instantly without mechanical lag. If you are still on an HDD, expect a long wait. It is just the reality of the hardware. ^[5]

When scans freeze: Troubleshooting common sticking points

It happens to the best of us - the scan reaches 92% and stays there for two hours. Usually, this is not a crash. The scanner is likely stuck on a very large compressed file, like a .ZIP or .ISO, or an encrypted folder. The software has to decompress these files in a temporary space to check their contents, which is incredibly resource-heavy.

If you are certain it is frozen, check your Task Manager. If the antivirus process is still showing CPU and Disk usage, it is still working. Let it be.

However, if usage is at 0% for over thirty minutes, you may need to restart the Windows Security service. I once spent three hours waiting for a scan that had actually crashed due to a disk read error. Now, I always check the Event Viewer if things seem suspicious. If the scan consistently fails at the same spot, you might have a corrupt sector on your drive that needs a chkdsk command to repair.

Beyond the basics: Scheduling and Offline scans

For those who want to be proactive without thinking about it, you can automate this process. Using the Windows Task Scheduler, you can set a full system scan to run every Sunday at 3 AM. This ensures your PC stays clean without interrupting your Monday through Friday workflow. Simply search for Task Scheduler, create a new task, and point it to the Windows Defender executable path.

There is also a nuclear option: the Microsoft Defender Offline scan. If you suspect a very stubborn virus is hiding within the operating system while it is running, this tool will restart your computer and run a scan before Windows even loads. This prevents malware from using - stealth - techniques to hide from the active scanner. It takes about 15 minutes and is one of the most effective ways to clean a heavily infected machine.

Choosing the right scan type

Quick Scan

• Low CPU usage; easy to do while working

• Typically 1-3 minutes

• Checks only common system startup folders and memory

Full Scan ⭐

• High CPU usage; best performed during downtime

• 30 minutes to 4 hours depending on drive type

• Every file, folder, and running process on all drives

Offline Scan

• Requires a full system restart; PC is unusable during scan

• Strictly 15 minutes

• Rootkits and persistent malware hiding in OS kernels

Alex's battle with a sluggish laptop

Alex, a freelance designer in Seattle, noticed his laptop was fans were spinning at max speed even when he was just browsing the web. He ran a Quick Scan, which found nothing, but the performance issues persisted and his browser started redirecting to odd sites.

He initiated a Full Scan but got frustrated when it hit 45% and stayed there for an hour. Assuming it was broken, he cancelled it and tried to install a third-party antivirus, which only made the lag worse as the two programs clashed.

He realized that the 'freeze' was likely just the scanner hitting his massive 500GB archive of design assets. He uninstalled the second antivirus, plugged his laptop into power, and let the Full Scan run overnight without interruption.

By morning, the scan had finished, identifying and removing two Trojan horses hidden in his old project folders. CPU usage dropped back to 5%, and his laptop felt brand new again after just 6 hours of patience.