Windows security and backups, in plain English · Updated October 3, 2026
You do not need a scary pop-up or a paid cleanup app to start checking a Windows PC. Begin with the protection tools already on the computer.
This guide describes Microsoft Defender Antivirus in Windows Security on a personal PC. If another provider is active, its scan controls may differ.
The quick answer
Open Windows Security from Start, choose Virus & threat protection, and start with a Quick scan. For a specific file or a wider concern, use Scan options. Read the results and any required action instead of assuming the progress bar tells the whole story.
Before starting
Save your work. Plug a laptop into power if you expect a lengthy check. Open the actual Windows Security app rather than clicking a web page that claims it has found a virus.
Confirm that Defender is the active antivirus provider, and check for protection updates. If the computer belongs to your employer or school, use its approved process.
Run the first check
- Open Start and search for Windows Security.
- Choose Virus & threat protection.
- Choose Quick scan if available.
- Let the scan finish and read the reported result.
If you are scanning because of a particular event, write down what happened and when. “I opened an unexpected attachment at 10:15” is more useful than “something feels wrong.”
Choose another scan for a reason
Under Scan options, a Full scan checks more broadly; a Custom scan lets you select files or folders. Microsoft Defender Offline restarts the PC to scan outside the normal Windows session. Save work before choosing it, and read its prompts.
An offline scan is different from simply turning off Wi-Fi. Review its results in Protection history after Windows returns. Microsoft documents these scan choices.
For ordinary maintenance, repeatedly launching the largest scan is not a useful substitute for keeping real-time protection and updates working.
If a threat is found
Read the detection name and recommended action in the security app. Complete any requested action or restart. Do not restore a quarantined item simply because you want to open it again.
If you think a detection is a mistake, verify the file’s origin and use official vendor support. Avoid creating a broad exclusion to silence a warning you have not understood.
If you entered account details into a suspicious page, treat that as an account problem too. A file scan cannot reverse a password you gave away.
If the scan is slow or fails
A large collection of files or archives can take time. Close unnecessary apps after saving work and check that the system drive has free space. Microsoft notes that insufficient space can interfere with quarantine and removal.
If the scan reports an error, record its wording. Update the protection tools and follow Microsoft’s scan troubleshooting guidance. Do not install an unknown “repair” utility offered by an advertisement.
What a clean result tells you
It tells you that scan did not report a threat in what it checked. It is useful evidence, but it is not proof that every account and file is safe.
If problems continue, narrow them down. A noisy fan during an update or a browser full of notifications needs a different investigation from a confirmed malware detection. Our signs of infection guide helps separate those situations.
Keep a record of the scan date, result, and any action taken. That makes a later support conversation much easier.
Official references
Technical details checked against these sources on October 3, 2026. App labels and included features can change.