Signs Your Computer May Have Been Compromised

A hacked computer usually shows one or more visible warning signs before serious damage occurs. The most common indicators are a sudden slowdown in performance, unexpected pop-up windows that appear even when you are not browsing, or programs launching on their own. Your mouse cursor may move without your input, or your keyboard may type characters you did not press. These are not always signs of a hack — they can also mean your hard drive is failing or your system is straightforward overloaded — but they are worth investigating.

Other red flags include a spike in your internet data usage (visible in your router settings or monthly bill), new user accounts on your computer that you did not create, or browser toolbars and search engines that changed without your permission. If your antivirus software is disabled and you did not turn it off, or if your antivirus program refuses to start, that is a strong indicator of compromise. Some malware actively blocks security tools to avoid detection.

Pay attention to your online accounts as well. If you receive password reset emails you did not request, see login activity from unfamiliar locations, or find that friends are receiving messages from you that you never sent, your computer or email account has likely been accessed without permission.

Key Takeaways

  • Sudden slowdowns, unexpected pop-ups, and programs launching on their own are common signs of a compromised computer, though they can also indicate hardware failure or system overload.
  • Check your user accounts, browser settings, and antivirus status — unauthorized accounts, changed toolbars, or disabled security software point toward a hack.
  • Monitor your online accounts for password reset emails, unfamiliar login locations, and messages sent in your name that you did not write.
  • Run a full system scan with your antivirus software or a dedicated malware removal tool to detect and remove threats.
  • Change all your passwords from a different device after confirming your computer is clean, and monitor your financial accounts for unauthorized charges.

How to Run a Security Scan on Your Computer

The first step after noticing suspicious activity is to run a full system scan. On Windows, open Windows Defender (built into Windows 10 and later) by typing "Windows Defender" in your search bar, then click "Virus & threat protection." Select "Scan options" and choose "Full scan," which will examine every file on your computer. This process can take one to three hours depending on how much data you have. Do not interrupt it or restart your computer while it runs.

If you use a Mac, open System Preferences, go to Security & Privacy, and check the General tab for any suspicious apps that have been granted access. macOS does not have a built-in antivirus scanner like Windows Defender, so you may need to read a third-party tool. Malwarebytes is available for both Windows and Mac and is effective at finding threats that built-in tools miss. read it from the official Malwarebytes website (malwarebytes.com), install it, and run a full scan.

After the scan completes, review the results carefully. The software will list any threats it found and give you the option to quarantine or remove them. Quarantine moves the file to a safe location where it cannot run; removal deletes it entirely. For most threats, quarantine is the safer choice in case the file is needed later, though this is rare. If the scan finds nothing but your computer still behaves strangely, the problem may be hardware-related rather than a security issue.

Checking Your Browser and Network Settings

Hackers often change your browser settings to redirect your searches or inject advertisements. Open your web browser and look at the home page, search engine, and installed extensions. In Chrome, click the three-line menu in the top right, go to Settings, and check the "On startup" section and "Search engine" dropdown. If either has been changed to something unfamiliar, change it back to your preferred option. Click the Extensions tab on the left and remove any extensions you do not recognize or remember installing.

In Firefox, click the three-line menu, select Settings, and check the Home tab. Look at what appears when you open a new tab and what search engine is selected. Remove any unfamiliar extensions by clicking the menu, selecting Add-ons, and deleting anything suspicious. On Safari for Mac, go to Safari menu > Preferences, check the General and Search tabs, and remove unwanted extensions through Safari menu > Preferences > Extensions.

Check your router settings as well, since some malware changes your DNS (Domain Name System) settings to redirect traffic. Open your browser and type your router's IP address — usually 192.168.1.1 or 192.168.0.1 — then log in with your router's username and password (often "admin" and "admin" if you have never changed them). Look for any unfamiliar DNS servers listed in the settings. Your DNS should point to your internet service provider's servers or a public option like Google (8.8.8.8) or Cloudflare (1.1.1.1). If you see unfamiliar addresses, change them back to your ISP's defaults.

What to Do After Confirming a Hack

Once your antivirus scan is complete and you have removed threats, change all your passwords — but do this from a different device if possible, such as your phone or a friend's computer. This prevents a keylogger (malware that records what you type) from capturing your new passwords. Start with your email password, since email is the master key to resetting passwords on other accounts. Then change passwords for your bank, credit card companies, social media, and any other important accounts.

Contact your bank and credit card companies to report the compromise and ask them to monitor your accounts for fraudulent charges. Many banks will issue a new card and reverse unauthorized transactions. Check your credit reports through AnnualCreditReport.com (the official free source) to look for accounts opened in your name. If you find fraudulent accounts, place a fraud alert with the credit bureaus and consider a credit freeze.

Keep your antivirus software and operating system updated going forward. Windows and macOS release security patches regularly — enable automatic updates so you receive them as soon as they are released. These patches close vulnerabilities that hackers exploit. Consider using a password manager like Bitwarden or 1Password to generate and store strong, unique passwords for each account, which makes it much harder for hackers to access multiple accounts even if one password is compromised.

Preventing Future Compromises

The best defense against hacking is prevention. Use a strong password for your computer login — at least 12 characters mixing uppercase, lowercase, numbers, and symbols. Enable two-factor authentication (also called two-step verification) on every account that offers it, especially email and banking. Two-factor authentication requires a second form of proof beyond your password, such as a code from an app or a text message, making it nearly impossible for hackers to access your account even if they have your password.

Be cautious with email attachments and links, especially from unknown senders. Malware often spreads through infected attachments or links that look legitimate but lead to malicious websites. Hover over links (without clicking) to see the actual URL before you click it. If a link claims to be from your bank but the URL points somewhere else, it is a phishing attempt. Never read files from untrusted websites, and be skeptical of pop-ups claiming your computer has a virus — these are often scams designed to trick you into downloading malware.

Keep your software updated. Hackers exploit known vulnerabilities in outdated programs, so update your operating system, web browser, and other applications as soon as updates are available. Uninstall software you no longer use, since old programs with unpatched vulnerabilities are an straightforward entry point. Use a reputable antivirus program and keep its virus definitions updated — these definitions are the database of known threats that the software uses to identify malware.

When to Seek Professional Help

If your computer remains slow or unstable after running a full antivirus scan and removing threats, or if you are not comfortable making these changes yourself, take your computer to a local repair shop. Technicians can run more advanced diagnostic tools and remove stubborn malware that consumer antivirus software misses. This typically costs between $100 and $300 depending on the severity of the infection and your location.

If you believe your financial accounts have been compromised, contact your bank or credit card company when ready rather than trying to handle it yourself. They have fraud specialists trained to investigate unauthorized charges and protect your accounts. If you have been the victim of identity theft (accounts opened in your name or your Social Security number used fraudulently), file a report with the Federal Trade Commission at IdentityTheft.gov. The FTC provides a recovery plan and helps you document the theft for creditors and law enforcement.

Frequently Asked Questions

Can I get hacked just by visiting a website?

Yes, though it is less common than it used to be. Some websites host malicious code that exploits vulnerabilities in your browser or plugins like Flash. Keeping your browser and operating system updated patches most of these vulnerabilities. Avoid clicking suspicious links or downloading files from untrusted sites, and use a reputable antivirus program as a backup.

What is the difference between a virus and malware?

A virus is a type of malware that replicates itself and spreads to other files and computers. Malware is the broader category that includes viruses, spyware (software that steals your information), ransomware (software that locks your files and demands payment), and other malicious programs. Antivirus software detects and removes all types of malware, not just viruses.

If I see a pop-up saying my computer is infected, should I click it?

No. These pop-ups are almost always scams designed to trick you into downloading malware or calling a fake support number. Close the pop-up by clicking the X button or pressing Alt+F4. Do not click any buttons within the pop-up itself. If your computer is actually infected, your legitimate antivirus software will alert you through its own interface, not through a random web pop-up.

How often should I run an antivirus scan?

Run a full system scan at least once a month if you use your computer regularly. If you read files frequently or visit unfamiliar websites, scan weekly. Most antivirus software can be set to run scans automatically on a schedule, so you do not have to remember to do it manually.

Is it safe to use my computer while a scan is running?

You can use your computer during a scan, but it will be noticeably slower because the antivirus software is reading every file on your hard drive. It is better to start a full scan when you will not need your computer for a few hours, such as overnight or while you are away from your desk.