Malware & Antivirus

Malware is malicious software designed to damage devices, steal information, spy on you or lock your files for ransom. It reaches people through email attachments, fake downloads, infected websites, bad apps and unpatched software. A few habits, such as updates, backups, careful downloads and antivirus, stop most of it.

• Everyone
• Families
• Small Business

Common types of malware

How infections happen

• Phishing emails and texts with malicious attachments or links. See Phishing and Smishing & Vishing.
• Fake or pirated software, cracked games and “free” tools, which often contain malware.
• Malicious ads and websites, including fake download buttons, fake virus warnings and drive-by downloads.
• Fake apps and extensions in app stores or from outside them. See App Permissions.
• Unpatched software: old operating systems and apps have known holes that attackers use.
• USB drives and charging ports from unknown sources. See USB & Public Charging Safety.
• Tech support scams that talk you into installing remote access software. See Tech Support Scams.
• Weak or reused passwords, which let attackers into accounts without malware.

Warning signs

• The device is suddenly slow, crashes or gets hot, or the battery drains faster than usual
• Pop-ups and ads appear when you aren’t browsing, or your browser homepage or search engine changed
• New apps, toolbars or extensions you didn’t install
• Files are locked, missing or renamed, or a ransom note appears
• Your accounts show unfamiliar logins, or friends receive messages you didn’t send
• The antivirus is turned off and won’t turn back on
• Unusually high data use or strange network activity

These can have other causes, but check anyway.

Antivirus and built-in protection

• Use real-time protection. Windows includes Microsoft Defender, macOS has built-in protections such as Gatekeeper and XProtect, and many phones scan apps. For many people, the built-in tools plus good habits are enough. Add a reputable security product if you want more features.
• Keep it on and updated, with automatic definition updates and regular scans.
• Don’t install more than one real-time antivirus. They can conflict. (Running a second one only for on-demand scans is fine.)
• Beware of fake antivirus. A pop-up that claims “Your computer is infected! Call now” or “Click to clean” is a scam. Close the browser and don’t call the number. Get security software only from the maker’s own site or an official store.
• Antivirus isn’t perfect. New malware can slip through. It works best with the other habits below.
• Business computers should follow IT policy, which may include managed endpoint protection. See Workplace Cybersecurity.

Habits that prevent most infections

• Update everything: operating system, browser, apps and router firmware. Turn on automatic updates. See Software Updates.
• Back up important files regularly, on an external drive and in the cloud. Keep one backup offline, since ransomware can encrypt connected drives. Test restores. See Backups.
• Download only from official sources (the maker’s website or the app store), and avoid pirated and cracked software.
• Think before you click. Don’t open unexpected attachments or links, even from known contacts, and check sender addresses.
• Use strong, unique passwords and two-factor authentication, with a password manager. See Passwords and Two-Factor Authentication.
• Use a standard account for daily use, not an administrator account, so malware can’t make deep changes.
• Limit apps and extensions, and review what you have installed, removing what you don’t use.
• Be careful on public Wi-Fi. See Public Wi-Fi and VPN Basics.
• Turn on SmartScreen or browser safe-browsing protection and use a pop-up blocker.

If you think you’re infected

1. Disconnect from the internet (unplug the cable or turn off Wi-Fi) to stop it from spreading or sending data.
2. Don’t pay a ransom before getting advice. Payment doesn’t guarantee getting files back, and it funds criminals. Report ransomware to the FBI’s Internet Crime Complaint Center (IC3) and to CISA.
3. Run a full scan with your security software, and an offline or second-opinion scanner if needed. Remove or quarantine what it finds.
4. Change passwords from a clean device, starting with email, banking and work accounts, and turn on two-factor authentication. See Hacked Accounts.
5. Tell your employer right away if it’s a work device or if work accounts may have been exposed.
6. Restore from a clean backup, or reset the device if the infection can’t be removed. Get help from a trusted technician if needed.
7. Watch your accounts and credit if personal information may have been stolen. See Identity Theft.

Phones and tablets

• Install apps only from the official app store, and check the developer and reviews.
• Be wary of apps that ask for permissions they don’t need. See App Permissions.
• Keep the operating system updated, and don’t jailbreak or root the phone.
• Don’t tap links in unexpected texts. Don’t install apps from links or “sideload” them.
• Turn on screen lock and “find my device.” See Smartphone Security.

Malware checklist

• Real-time antivirus or built-in protection is on and updated
• Operating system, browser and apps update automatically
• Important files are backed up, with one copy offline
• I download only from official sources and don’t open unexpected attachments
• I use strong unique passwords with two-factor authentication
• I know to disconnect, scan, change passwords and report if infected

Last updated: October 4, 2026