A sluggish computer, strange pop-ups, or programs you don’t remember installing — these could all be signs that your computer is infected with malware. In an age where we rely on our devices for everything from online banking to remote work and entertainment, recognizing the warning signs of infection is more important than ever. Here’s how to tell if your computer might be compromised — and what you can do about it.

When Your Computer Suddenly Slows Down

One of the most common signs of infection is a noticeable slowdown. Programs take longer to open, your browser freezes, or even simple tasks like opening a folder feel delayed. This can happen when malicious software runs in the background, consuming your system’s resources.

If you notice this, open Task Manager (Windows) or Activity Monitor (Mac) to see which programs are using the most CPU or memory. Unknown processes with odd names can be a red flag.

Unexpected Pop-Ups and Ads

If you start seeing ads even when you’re not browsing the web, or pop-ups warning you about “viruses” and urging you to install a program, be cautious. Many of these alerts are fake and designed to trick you into downloading more malware.

Never click “OK” or “Close” inside the pop-up itself. Instead, use Alt + F4 (Windows) or Cmd + Q (Mac) to safely close the window.

Unknown Programs and Changed Settings

Have you noticed new programs, browser toolbars, or changed startup settings that you didn’t authorize? Some types of malware modify your homepage, alter search results, or install extensions that track your activity.

Regularly review your installed programs and remove anything unfamiliar. On Windows, go to Settings → Apps; on Mac, check your Applications folder.

Overheating and Loud Fans

If your computer suddenly gets hot or the fan runs constantly, it could be under strain from hidden processes. Some malware uses your computer’s power to mine cryptocurrency or send spam without your knowledge, which increases both fan noise and energy use.

If this happens, run a full system scan with an up-to-date antivirus program right away.

Suspicious Network Activity

Unusual network activity can also signal infection. If your internet connection is slow even when you’re not using it, malware might be sending data in the background. You can check this by viewing your network usage in your antivirus software or system settings.

Also, pay attention if your firewall reports that unknown programs are trying to access the internet without your permission.

Strange Emails or Account Activity

If friends report receiving odd messages from you, or you notice logins from unfamiliar locations, your computer or accounts may be compromised. Change your passwords immediately and enable two-factor authentication wherever possible.

It’s also wise to scan your system for keyloggers — malicious programs that record your keystrokes and send them to hackers.

Læs også:

The biggest threats to your devices – and how to protect yourself from them

Units

Our devices hold more of our personal and financial information than ever before—making them prime targets for cybercriminals. Learn about the most common digital threats and discover practical ways to protect your data, privacy, and peace of mind.

Take Good Care of Your Tech: How to Transport Your Devices Safely

Units

Your devices go everywhere with you—make sure they stay protected. Learn how to pack, carry, and care for your tech the right way, from choosing the best bag to safeguarding your data on the go.

Is Your Computer Infected? How to Recognize the Warning Signs

Units

Is your computer acting strangely? From sudden slowdowns to mysterious pop-ups, these symptoms could mean your system is infected. Discover the most common warning signs of malware and what steps you can take to protect your data and devices.

Cases and Covers: Which Materials Offer the Best Protection?

Units

From silicone to metal, every case material offers different levels of protection and style. Learn which options best safeguard your phone, tablet, or laptop—and what to consider before choosing your next cover.

How to Protect Yourself Going Forward

Prevention is the best defense. Here are some simple steps to stay safe:

• Keep your system and software updated — many infections exploit known security flaws.
• Use reputable antivirus software and make sure it updates automatically.
• Be cautious with emails and links — never open attachments from unknown senders.
• Back up your data regularly so you can recover it if something goes wrong.
• Use strong, unique passwords and consider a password manager to keep them secure.

By combining smart digital habits with solid technical protection, you can reduce your risk of infection and catch problems early.

When the Damage Is Done

If you suspect your computer is already infected, take these steps:

1. Disconnect from the internet to prevent further data leaks.
2. Run a full system scan with your antivirus software.
3. Quarantine or remove any suspicious files.
4. Update your operating system and all applications.
5. Seek professional help if the issue persists.

In severe cases, you may need to reinstall your operating system to ensure the infection is completely removed.

A Healthy Computer Starts with Awareness

Most infections can be avoided if you stay alert to changes in your computer’s behavior. Pay attention to the small signs — a slower startup, a new toolbar, a constantly running fan — and act quickly. The sooner you respond, the less damage malware can do.