Malware is malicious software designed to harm a device, steal information, disrupt activity, or gain unauthorized access. Viruses, ransomware, spyware, worms, and Trojan horses are all types of malware. A slow device or unexpected pop-up can be a clue, but symptoms alone do not prove infection; ordinary software or hardware problems can look similar.
What is malware?
Malware is short for malicious software. It describes software created or used to damage a device, interfere with its operation, spy on a user, or access information without permission. A Trojan horse is malware that disguises itself as a legitimate file or app to persuade someone to run it. CISA explains common malware forms and risks.
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Common types of malware
- Viruses: Malicious code that can attach to files or programs and spread when they are run or shared.
- Ransomware: Malware that can block access to files or systems, often by encrypting data, and demand payment.
- Spyware: Software that secretly collects information about a user or their activity.
- Worms: Malware that can spread between systems, often across networks, without needing to attach itself to another program.
- Trojan horses: Files or apps that pretend to be legitimate so a person will install or run them.
How do I know if my device has malware?
Possible warning signs include an abrupt slowdown, shorter battery life, unexplained data use, frequent pop-ups, browser redirects, repeated errors, security tools that stop working, or messages sent from your accounts without your knowledge. These symptoms are clues, not a diagnosis. Hardware faults and ordinary software issues can cause similar behavior, as Microsoft notes in its guidance on checking for malware.
Be especially cautious if a security warning appears in a webpage or pop-up and urges you to call a number, install a tool, or pay immediately. Do not use the pop-up as your source for a removal app; use the security tools already on your device or get help from a manufacturer or support provider you know and trust.
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What should I do first if I suspect malware?
- Stop sensitive activity on the suspected device. Do not use it to sign in to banking, shopping, email, or other important accounts while you assess the issue. The U.S. Federal Trade Commission (FTC) advises: “Immediately stop logging into online accounts with your usernames, passwords, or other sensitive information — like shopping or banking.” This is from its consumer guidance, “Malware: How To Protect Against, Detect, and Remove It,” dated April 2025.
- Protect accounts from a separate, known-clean device if needed. If you have reason to believe credentials or accounts were exposed, prioritize changing the affected passwords and enabling two-factor authentication from that clean device.
- Run the appropriate built-in security check. On Windows, update security intelligence and run a full scan if you suspect infection. On a Mac, follow Apple’s instructions if macOS identifies a malicious download. Mobile-device instructions depend on the operating system and version; use the platform maker’s current guidance rather than Windows steps.
- Follow the security tool’s result. If it detects a threat, use its remove or quarantine option. Quarantine blocks a file from running. Do not choose to allow a detected item unless you trust both the software and its publisher.
- Get trusted help if the problem continues. Contact your device maker or a support provider you already trust rather than downloading a remover from an advertisement or an unfamiliar site.
How do I remove malware on Windows or Mac?
The correct approach depends on the operating system. Windows and macOS have built-in protections, but their scan and removal steps are not interchangeable. Menu labels can change with operating-system updates, so check the current security settings on your device.
| Question | Windows | Mac |
|---|---|---|
| Built-in protection | Microsoft Defender Antivirus and Windows Security provide scanning and threat-handling options. | macOS includes Gatekeeper, notarization, and XProtect. Apple says XProtect can detect and remove known malware; features vary by macOS version. |
| How the scan runs | A full scan runs in the regular Windows environment. Microsoft Defender Offline restarts the device and scans without loading Windows, which can make persistent malware harder to hide. | Apple’s cited guidance describes built-in protections and handling a flagged download; it does not prescribe a comparable separate restart-based scan. |
| If a file is flagged | Follow Windows Security’s remove or quarantine instructions. Quarantine blocks the file from running; allow it only if you trust the software and publisher. | Do not open a download that Apple identifies as malware. Move it to the Bin and empty the Bin, following Apple’s guidance for avoiding or removing malware. |
| When to get support | If the threat remains after scanning, or you cannot complete a scan, contact the device maker or a trusted support provider. | If a warning or symptoms persist after following Apple’s instructions, contact Apple or a support provider you know and trust. A paid scanner is not automatically required. |
Windows: run a full scan, then consider Defender Offline
A quick scan is useful for routine checks, but Microsoft recommends a full scan when you believe your PC is infected. Open Windows Security, go to Virus & threat protection, and choose the scan options to start a full scan. Update security intelligence first if an update is available. The precise menu wording may vary by Windows version and product updates.
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If a persistent threat is not resolved by a normal scan, Microsoft Defender Offline is another option. It restarts the computer and scans in a separate environment without loading Windows; the computer restarts again when the scan finishes. Save open work before starting because the scan requires a restart. See Microsoft’s Defender Offline instructions.
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Mac: follow the malware alert and Apple’s removal guidance
macOS uses Gatekeeper and notarization to help prevent untrusted or known-malicious apps from running, along with XProtect for detecting and remediating known malware. If Apple identifies a downloaded item as malware, do not open it; move it to the Bin and empty the Bin. Follow Apple’s current malware guidance. A browser pop-up by itself does not establish that a Mac is infected.
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Phones and tablets: use the platform maker’s current instructions
Malware can affect phones and tablets as well as computers, but the steps depend on the device and operating-system version. Do not apply Windows scan instructions to a phone. Consult the maker’s current security guidance; if an account may be exposed, use a separate clean device to secure it.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What if ransomware is active?
If ransomware is actively affecting a device, disconnect that system from networks to limit further spread or communication. This is a ransomware-specific containment step, not a general response to every unexplained slowdown or pop-up. CISA’s ransomware guidance recommends network disconnection and careful handling of recovery. Before restoring files, check that the backup is safe to use. Paying a ransom does not guarantee recovery.
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What should I do after malware is removed?
- Change exposed passwords and enable two-factor authentication. Use a known-clean device if the affected one may still be compromised.
- Review important accounts. Look for unfamiliar sign-ins, messages, purchases, or changes to account settings, and follow the service’s recovery process if something is wrong.
- Act on possible identity theft. In the United States, the FTC directs people whose identity information may have been stolen to IdentityTheft.gov. Reporting and recovery services differ by country.
- Seek reputable technical help if symptoms persist. The FTC recommends contacting the device manufacturer or a company you know and trust. Avoid tools promoted through alarming pop-ups or unknown advertisements.
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