How to Check Your Computer for Malware

Malware doesn't always announce itself. Sometimes your computer slows to a crawl, shows unexpected pop-ups, or starts behaving strangely. Other times, it runs silently in the background, logging keystrokes or siphoning files without any obvious sign. Knowing how to check your computer for malware — and understanding what that process actually involves — is one of the most practical security skills you can build.

What Malware Actually Does (And Why It's Hard to Spot)

Malware is a broad term covering any software designed to damage, disrupt, or gain unauthorized access to a system. This includes viruses, trojans, ransomware, spyware, adware, and rootkits — each behaving differently and requiring slightly different detection approaches.

Some malware is loud: ransomware locks your files and demands payment immediately. Other types are engineered to be invisible. Spyware and keyloggers are specifically designed to avoid detection while collecting data over weeks or months. Rootkits embed themselves deep in the operating system, sometimes at the firmware level, making them especially difficult to find with standard tools.

This range in behavior is exactly why a single scan isn't always enough.

Built-In Tools: Your First Line of Defense

Both Windows and macOS ship with native security tools that handle a significant portion of everyday malware detection.

On Windows, Windows Security (formerly Windows Defender) includes a real-time protection engine and an on-demand scanner. To run a scan:

• Open Windows Security from the Start menu
• Go to Virus & threat protection
• Select Quick scan for a fast check of common infection points, or Full scan for a thorough sweep of every file on the drive

A Quick scan typically checks running processes, startup items, and common system folders. A Full scan goes deeper and takes considerably longer — sometimes hours on large drives. There's also an Offline scan option that restarts your PC and scans before Windows fully loads, which is useful for catching malware that hides during normal operation.

On macOS, Apple's XProtect runs silently in the background and checks files against a known malware database when they're opened or downloaded. Gatekeeper adds a layer by blocking apps from unidentified developers. These tools are passive — they don't offer a manual "scan now" button in the way Windows Security does.

Third-Party Scanners: When to Bring in Backup 🔍

Built-in tools are competent but not exhaustive. Third-party malware scanners use different detection databases and behavioral analysis engines, which means they can catch threats that built-in tools miss — and vice versa.

Running a second-opinion scanner alongside your existing protection is a common and sensible practice. These tools are designed to be used on demand rather than running continuously, so they don't conflict with your primary antivirus.

Key things these scanners typically check include:

• Running processes — active programs in memory, flagging anything exhibiting suspicious behavior
• Startup entries — programs configured to launch automatically on boot
• Browser extensions — a common hiding spot for adware and hijackers
• Registry entries (Windows) — where malware often embeds persistence mechanisms
• Temporary file folders — frequently used as staging grounds for malicious payloads

Signs Your Computer May Be Infected

Not every malware infection announces itself, but common indicators include:

If you're seeing multiple symptoms simultaneously, the likelihood of an active infection increases significantly.

How to Do a Thorough Manual Check

Automated scanners catch most threats, but a manual review of a few key areas adds a meaningful extra layer.

Check startup programs. On Windows, open Task Manager and navigate to the Startup tab. Any unfamiliar program set to launch at boot deserves investigation. On macOS, go to System Settings → General → Login Items.

Review installed applications. Look through your list of installed programs for anything you don't recognize. Malware occasionally installs as a seemingly legitimate app with a generic or slightly misspelled name.

Inspect browser extensions. Open your browser's extension manager and audit every installed extension. Remove anything you didn't deliberately install or no longer use.

Monitor network activity. Tools like Resource Monitor (Windows) or Activity Monitor (macOS) can show which processes are making network connections. Unexpected outbound connections to unfamiliar IP addresses are worth flagging.

The Variables That Shape Your Approach 🛡️

How you check for malware — and how thorough you need to be — depends on several factors that vary from user to user.

Operating system and version matter considerably. Older versions of Windows without recent security patches have known vulnerabilities that make infections more likely and harder to clean. macOS faces a narrower but growing threat landscape.

How the computer is used affects risk level. A machine used exclusively for streaming media has a different exposure profile than one used for downloading files, running software from unverified sources, or handling sensitive financial data.

Technical comfort level determines how far you can reasonably go. Running a basic scan in Windows Security is accessible to nearly anyone. Analyzing network traffic, inspecting registry entries, or removing a rootkit manually requires significantly more expertise — and mistakes during manual removal can cause additional damage.

Severity of the suspected infection also shapes the response. A browser hijacker and a deeply embedded rootkit require very different remediation strategies. Some infections are cleanable; others — particularly advanced ransomware or firmware-level malware — may necessitate a full system wipe and reinstall to be certain the machine is clean.

What a thorough check looks like for your machine ultimately comes down to your specific setup, the symptoms you're seeing, and how deep you're willing or able to go.