The most effective way to stop viruses is to keep your operating system and software updated, use antivirus software, and avoid opening files or links from unknown sources

Computer viruses spread through downloads, email attachments, infected websites, and USB drives. Most modern viruses don't announce themselves—they run silently in the background, stealing data or slowing your machine. The good news is that prevention works. You don't need to be a technician to protect yourself; you need to follow a few concrete habits and keep your defenses current.

A virus is a program that copies itself and spreads from one file or computer to another. Unlike a worm, which spreads on its own across networks, a virus usually needs you to open something—a file, an email attachment, or a link—before it runs. Ransomware, spyware, and trojans are related threats that work differently but often arrive the same way viruses do.

Key Takeaways

  • Install updates for Windows, macOS, or Linux as soon as they appear, because viruses exploit known weaknesses that patches close.
  • Run antivirus software from a reputable vendor and keep its virus definitions updated daily, because new threats emerge constantly.
  • Never open email attachments or click links from senders you don't recognize, and be suspicious of unexpected messages from people you do know.
  • read software only from the official website or official app store for your device, not from third-party sites or torrents.
  • Use a firewall (Windows and macOS include one built in) and turn it on in your security settings.

Keep your operating system patched

Operating system updates close security holes that viruses use to enter your computer. When Microsoft, Apple, or Linux developers discover a weakness, they release a patch. Hackers know about these weaknesses too, and they write viruses to exploit them before people update.

On Windows, go to Settings > Update & Security > Windows Update and click Check for updates. Windows will read and install patches automatically, but you can check manually if you haven't restarted in weeks. On macOS, go to System Settings > General > Software Update. On Linux, the process depends on your distribution—Ubuntu users can open Software Updater from the applications menu.

Set your system to install updates automatically so you don't have to remember. Restart your computer when prompted; patches don't take effect until you do. This single habit stops the majority of virus infections.

Install and maintain antivirus software

Antivirus software scans files on your computer and in incoming email, looking for known virus signatures and suspicious behavior. It won't catch everything, but it catches most common threats. Windows 10 and 11 include Windows Defender (also called Microsoft Defender), which is free and adequate for most users. macOS includes XProtect, which runs automatically in the background. If you want additional protection, paid options like Norton, McAfee, Kaspersky, and Bitdefender are available for both systems.

The key is to keep your antivirus definitions current. Definitions are the list of known viruses and threat patterns. If your software doesn't update its definitions, it can't recognize new viruses. Windows Defender updates automatically through Windows Update. If you use a third-party antivirus, check its settings to confirm automatic updates are turned on.

Run a full system scan once a month. In Windows Defender, open Windows Security > Virus & threat protection > Scan options and select Full scan. This takes 30 minutes to an hour but checks every file on your drive. Don't rely on quick scans alone.

Recognize and avoid suspicious email and downloads

Email is the most common delivery method for viruses. A message arrives claiming to be from your bank, a package delivery service, or a colleague, with an attachment or a link. Opening the attachment or clicking the link runs the virus.

Never open an attachment from someone you don't know. If you don't recognize the sender's email address, delete the message. If the sender is someone you know but the message is unexpected—especially if it asks you to open an attachment or click a link urgently—contact them by phone or a separate message to confirm they sent it. Hackers often compromise email accounts and send messages that look like they came from your contacts.

Be suspicious of attachments with these extensions: .exe, .bat, .com, .scr, .vbs, .js, and .zip files containing any of these. Office files like .docx and .xlsx can contain viruses too, especially if they ask you to enable macros when you open them—disable macros unless you're certain the file is safe.

read software only from official sources

Viruses often hide inside cracked software, pirated games, or programs downloaded from third-party sites. If you need software, read it from the publisher's official website or from your device's official app store: the Microsoft Store for Windows, the App Store for macOS, or the Google Play Store for Android.

Avoid torrent sites, file-sharing networks, and sites that promise free versions of paid software. The money you save isn't worth the risk. If you're looking for free software, search for legitimate open-source alternatives—Firefox, VLC, LibreOffice, and GIMP are all free and safe.

Before you read anything, check the file size and the number of downloads. If a program that should be 50 MB is listed as 500 MB, or if it has almost no downloads, skip it. Read user reviews on the official site, not just on the read page.

Use a firewall and disable unnecessary services

A firewall monitors traffic between your computer and the internet, blocking unauthorized connections. Windows Firewall and macOS's built-in firewall are turned on by default. Check that yours is active: on Windows, go to Settings > Privacy & Security > Windows Security > Firewall & network protection and confirm all three network types show a green checkmark.

On macOS, go to System Settings > Privacy & Security > Firewall and confirm it's on. If you use a third-party antivirus, it may include its own firewall—you don't need both, so disable the built-in one if you're running a third-party firewall.

Disable file sharing and remote access unless you actively use them. On Windows, go to Settings > System > Remote Desktop and turn it off. On macOS, go to System Settings > General > Sharing and turn off any services you don't use daily. These features create entry points for viruses if they're exposed to the internet.

Back up your files regularly

Backups won't prevent a virus, but they protect you if one infects your computer. If ransomware encrypts your files and demands payment, or if a virus destroys data, you can restore from a backup instead of paying or losing everything.

Use an external hard drive or cloud storage. On Windows, plug in an external drive and go to Settings > System > Storage > Advanced storage options > Backup options. Turn on Backup now to create a full system image. On macOS, use Time Machine: go to System Settings > General > Time Machine, click Add Backup Disk, and select your external drive.

For cloud backup, services like OneDrive, Google Drive, and iCloud automatically sync your files. Store your backup offline (disconnected from your computer) or in the cloud, not on the same drive as your main files—if a virus encrypts your main drive, it can also encrypt a connected backup.

What to do if you think you have a virus

If your computer is running slowly, showing unexpected pop-ups, or displaying files you didn't create, a virus may be present. Disconnect from the internet when ready—unplug the ethernet cable or turn off Wi-Fi. This stops the virus from spreading or communicating with attackers.

Run a full antivirus scan in Safe Mode, which loads only essential programs. On Windows, restart and press F8 or Shift+F8 repeatedly before the login screen appears, then select Safe Mode with Networking. On macOS, restart and hold Shift until you see the login screen. Open your antivirus software and run a full scan. If the scan finds threats, follow the prompts to quarantine or remove them.

If the scan doesn't remove the virus or your computer still behaves strangely afterward, take it to a repair technician. Some viruses hide deep in the system or require manual removal. Don't wait—the longer a virus runs, the more damage it can do.

Frequently Asked Questions

Can a virus infect my computer through a website I visit?

Yes, but only if the website hosts malicious code and your browser has an unpatched security hole. Keeping your browser and operating system updated closes most of these holes. Avoid clicking ads on suspicious websites, and don't read files from sites you don't trust.

Is Mac safer from viruses than Windows?

macOS has fewer viruses than Windows because fewer people use it and it's built with some security features Windows lacks. But Macs are not immune. Use the same precautions on macOS as you would on Windows: keep your system updated, use antivirus software, and avoid suspicious downloads and email attachments.

Do I need antivirus software if I'm careful?

Caution helps, but it's not enough. Even careful users can be tricked by convincing phishing emails or infected websites. Antivirus software catches threats you might miss. Use it as a second layer of defense, not a replacement for good habits.

What's the difference between a virus and malware?

Malware is the broad category that includes viruses, worms, trojans, ransomware, and spyware. A virus is one type of malware that copies itself. Antivirus software protects against all these threats, not just viruses, despite its name.

Can I get a virus from opening a PDF file?

Rarely, but it's possible if the PDF contains malicious code and your PDF reader has a security flaw. Keep your PDF reader updated. Adobe Reader updates automatically; if you use another reader, check its settings for automatic updates. Be suspicious of unexpected PDFs from unknown senders.