Free Guide to Checking Your Device for Viruses

Understanding Computer Viruses and Malware

A computer virus is a type of malicious software, often called malware, that can harm your device and personal information. Unlike biological viruses, computer viruses spread through files, programs, and networks rather than through the air. According to Statista's 2024 cybersecurity report, over 450 million malware samples are detected globally each month, showing how common these threats have become.

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Viruses work by attaching themselves to legitimate programs or files. When you run an infected program, the virus activates and can perform unwanted actions like stealing passwords, displaying advertisements, or corrupting your files. Other types of malware include worms, which spread on their own without needing a host program, and trojans, which disguise themselves as harmless software but carry hidden threats.

Different malware types have different characteristics. Ransomware locks your files and demands payment to unlock them. Spyware secretly monitors your online activity and keyboard input. Adware floods your screen with unwanted advertisements. Rootkits hide deep in your system to avoid detection. Browser hijackers change your homepage and search engine without permission.

Your device can catch viruses through many routes: downloading files from unsafe websites, opening email attachments from unknown senders, visiting compromised websites, using infected USB drives, or downloading programs from unofficial sources. Mobile devices running Android or iOS can also contract malware, though at lower rates than computers.

Practical takeaway: Knowing what malware does and how it spreads helps you recognize risks. Viruses rarely cause problems on their own—they need you to take an action like opening a file or clicking a link. Understanding this means you can reduce your risk through careful behavior with files and links from unknown sources.

Signs Your Device May Be Infected

Recognizing symptoms of a virus infection is your first line of defense. The most common sign is a significant slowdown in performance. If your computer takes much longer to start up, programs load slowly, or everything feels sluggish, malware may be consuming your system's resources. However, slowness can also result from a full hard drive, outdated software, or a device that's simply aging, so this sign alone doesn't confirm infection.

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Unexpected pop-ups represent another major warning sign. If your browser shows advertisements or pop-ups even when you're not browsing websites, or if pop-ups appear when your browser is closed, malware may be present. Legitimate websites occasionally use pop-ups, but constant unwanted pop-ups—especially ones trying to sell antivirus software or other products—often indicate infection.

Changes to your device that you didn't make are serious red flags. These include:

• Your homepage or search engine changed without your action
• New toolbars or extensions appear in your browser
• Your mouse cursor behaves strangely or moves on its own
• Programs start automatically when you boot your device
• New files or folders appear in unexpected locations
• Your device restarts repeatedly on its own
• Your internet connection drops frequently

Network activity problems can signal malware. If your internet usage suddenly increases (visible through your internet service provider's data tracking or your router's monitoring), even when you're not actively using the internet, a virus might be sending data in the background. Some malware operates botnets, using your device to attack other computers without your knowledge.

Other signs include unusual error messages you've never seen before, programs crashing frequently, your antivirus software being disabled or behaving strangely, or security warnings appearing constantly. Your device may also get very hot or your fans may run constantly as malware consumes processing power.

Practical takeaway: No single symptom definitively proves infection—many computer problems have innocent explanations. However, several symptoms together make infection more likely. If your device shows multiple warning signs, it's worth scanning even if you're not certain.

Using Built-In Security Tools on Your Device

Most devices come with basic security tools already installed, and learning to use them is your first option for checking for viruses. These built-in tools are legitimate security features created by your device's manufacturer and are reliable for detecting common threats.

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Windows devices include Windows Defender (also called Microsoft Defender), which provides real-time scanning and malware detection. To run a full scan on Windows 10 or 11, open the Start menu, type "Windows Security" and select it, then click "Virus & threat protection." Choose "Scan options" and select "Full scan," which examines your entire device. A full scan typically takes 30 minutes to several hours depending on your device's size and speed. Windows Defender works quietly in the background by default, but you can check its status anytime through the Windows Security app.

Mac devices use XProtect, a built-in malware detection system that works automatically. Macs also include Gatekeeper, which verifies that programs come from trusted sources before allowing them to run. If you want to manually scan your Mac, you have fewer options than Windows users since macOS doesn't offer a built-in manual scanning tool like Windows does. However, XProtect scans files automatically when they're downloaded and opened.

Linux users benefit from the Linux kernel's design, which makes virus infection less common. Most Linux distributions don't require antivirus software, though scanning tools exist if you want additional security.

Mobile devices also have built-in protection. Android devices have Play Protect, which scans apps from the Google Play Store and regularly checks installed apps for threats. Access this by opening Google Play Store, tapping your profile icon, selecting "Manage apps & device," going to the "Manage" tab, and tapping "Play Protect." iOS devices use automatic scanning and code review but don't provide manual scanning options to users.

Practical takeaway: Starting with your device's built-in security tools costs nothing and requires no installation. Run a full scan at least monthly, or whenever you notice suspicious symptoms. These tools won't catch every threat, but they handle the majority of common infections effectively.

Installing and Using Third-Party Antivirus Software

If you want additional scanning capability beyond your device's built-in tools, third-party antivirus software offers more features and regular updates. Many reputable antivirus companies offer free versions of their software alongside paid premium versions. Free versions typically provide basic scanning and real-time protection, while paid versions add features like 24/7 monitoring, firewall protection, and ransomware blocking.

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Popular free antivirus options include Avast Free Security, AVG AntiVirus Free, and Bitdefender Antivirus Free. These are available from the companies' official websites and from legitimate software distribution platforms. Avoid downloading antivirus software from unknown websites, as malware often disguises itself as security software—a threat called "scareware" that tricks you into thinking you need to purchase fake protection.

When installing antivirus software, follow these steps carefully. First, download the software only from the official company website or established software stores you recognize. Second, close your web browser and other programs before installation. Third, follow the installation prompts exactly as shown. Fourth, allow the program to update its virus definitions (the list of known threats) after installation. Fifth, run an initial full scan before using the software for regular monitoring.

After installation, set the software to scan on a regular schedule—weekly or monthly depending on your usage. Most antivirus programs allow you to schedule automatic scans at times when you're not using your device. Some programs may slow your device during scans, so scheduling them during nights or weekends helps minimize disruption.

Important caution: Installing multiple full antivirus programs on one device can cause conflicts and slowdowns. If you already have one antivirus program running, remove it before installing another. Using your device's built-in protection with one additional third-party tool is better than running multiple programs simultaneously.

Practical takeaway: Third-party antivirus software provides more scanning options than built-in tools, but requires installation and uses system resources. Choose one reputable program from a known company, install it only from the official source, and keep it updated for best protection.

Performing Manual Scans and Interpreting Results

Once you have scanning software installed, understanding how to run different types of scans helps you target potential problems. Most

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