How do I run a full system scan on my PC?

How to run a full system scan on PC safely

how to run a full system scan on PC helps detect hidden threats that slow performance and affect system security. A complete scan checks more areas than a quick review and supports better protection for files and installed programs. Understanding the correct scan process reduces confusion during Windows security checks and helps maintain stable computer performance.

How to run a full system scan on PC using Windows Security

Running a full system scan is the digital equivalent of a deep spring cleaning for your computer. To start, open Windows Security by clicking the Start menu and typing its name. Navigate to Virus & threat protection, click on Scan options - not the big button that says Quick Scan - then select Full scan and hit Scan now. This process examines every single file, folder, and running program on your hard drive to ensure no malware is lurking in the shadows.

Full scans are intensive. Unlike quick scans that only check common hiding spots, a full scan typically inspects a large number of files and can take anywhere from 1 to several hours depending on your drives speed and data volume. ^[2] It is thorough. It is deep. It is also quite slow. I once started a scan at noon and was still watching the progress bar crawl at dinner time. But for peace of mind, that wait is worth it.

A Step-by-Step Guide for Windows 11 and 10

The interface for Windows Security is fairly consistent across modern versions of the operating system. Follow these steps to ensure you are doing it correctly: 1. Press the Windows Key and type Windows Security. 2. Open the app and select the Virus & threat protection tile. 3. Look for the blue text link labeled Scan options located just under the current threat status. 4. Select the radio button for Full scan. 5. Scroll down and click the Scan now button.

Most modern antivirus solutions, including the built-in Windows tools, now achieve high detection rates for known threats, ^[1] so the accuracy is high even if the speed is not. But there is one specific mistake people make with external drives that can leave a back door open - more on that in the advanced settings below.

Understanding the different scan types: Which one do you need?

Not all scans are created equal, and choosing the wrong one can either waste your time or leave your PC at risk. While the full scan is the gold standard for thoroughness, it is not always the practical choice for a Tuesday afternoon. You need to know when to bring out the heavy machinery and when a quick check is enough. Sometimes, even a full scan cannot find a virus if the malware is integrated into the boot process, which is where the offline malware scan Windows 11 becomes your best friend.

In my early days of troubleshooting, I used to run full scans daily. It was overkill. My PC spent more time scanning than actually working. I eventually learned that a quick scan catches most active threats because most malware targets specific, high-traffic system folders. ^[4] However, if your PC is acting sluggish or showing pop-ups, the quick scan is no longer sufficient. You must go deep.

Why is my full scan taking so long?

Performance impact is the biggest deterrent for users. During a full scan, your system experiences increased CPU usage^[3] as the antivirus engine opens and reads thousands of compressed files. This can make gaming or video editing feel jittery. If you are using an older mechanical Hard Disk Drive (HDD), the impact is even more noticeable than on a modern Solid State Drive (SSD).

The sheer number of files is the primary factor. If you have years of old photos, installers, and game backups, you might be asking the software to check over 2 million individual items. This is why the scan feels like it is stuck at 80% or 90% - it is likely chewing through a particularly dense folder of small files or a massive archive.

Be patient. Let it finish. If you cancel it midway, you gain nothing. The software does not remember where it left off in a way that makes a subsequent scan faster. It is an all-or-nothing commitment.

Advanced scanning: Network and removable drives

Here is the kicker: a standard full scan often ignores your external backup drives and mapped network storage unless you tell it otherwise. This is a massive security gap. Malware is smart. It often copies itself to your USB thumb drive or NAS (Network Attached Storage) so that even if you wipe your PC, the infection returns as soon as you plug your drive back in.

To fix this, you should use the Custom scan option found in the same menu as the full scan. This allows you to check specific drives. I recommend running a full scan on your main OS drive first, followed by a separate custom scan on any permanently attached external storage. It takes longer, but it closes the loop. This ensures that roughly 100% of your data environment is verified clean, rather than just the primary system files.

Troubleshooting: What if the scan gets stuck?

It happens to the best of us. You leave the scan running overnight, and you wake up to find it frozen at 92%. Frustrating? Absolutely. Usually, this is not a software crash but a conflict with a specific file that the antivirus cannot open, such as a corrupted system file or a protected archive.

If your scan hangs for more than 5 hours without moving a single percentage point, it is time to intervene. First, try restarting your PC and running the scan again. If it stops at the exact same spot, note the file path displayed on the screen. You may need to manually exclude that folder or delete the corrupted file. For truly stubborn infections that prevent scans from finishing, the Microsoft Defender full scan instructions and using the Windows Security scan options guide are your best bet. It runs before Windows even starts, meaning the malware has no chance to interfere with the scanning process.

Choosing the right scan for your situation

Windows Security provides multiple ways to protect your PC. Choosing the right one depends on your symptoms and the time you have available.

Quick Scan

• Best for routine daily checks
• 2 to 5 minutes
• Only checks folders where threats are commonly found

Full Scan ⭐

• Best if you suspect an infection or do monthly maintenance
• 1 to 4 hours
• Checks every single file and program on the hard drive

Microsoft Defender Offline

• Best for stubborn malware that hides from the OS
• 15 minutes (requires restart)
• Scans the boot sector and system files before Windows loads

Mark's Battle with the Infinite Progress Bar

Mark, a graphic designer in Seattle, noticed his PC was acting sluggish and opening random browser tabs. He ran three quick scans, but they all came back clean. He was confused and worried that his client files were at risk.

He decided to run a full scan before bed. The next morning, he found the scan stuck at 88%. It had been sitting there for five hours. He almost forced a shutdown in frustration, thinking his hardware was failing.

Instead of quitting, he realized his 4TB external backup drive was still plugged in. He stopped the scan, unplugged the drive, and ran a full scan on just the primary SSD. He realized the software was struggling with millions of tiny icon files on his backup.

The new scan finished in 45 minutes and found 3 trojans. After the cleanup, his PC speed improved by roughly 40%. He learned to scan his OS drive and backups separately to avoid the 'infinite' hang.