Is Your PC Infected? 7 Warning Signs Your Computer Has a Virus

Introduction: The “Is It a Virus or Is My PC Just Old?” Hook

It’s one of the most frustrating feelings in modern life. Your once-speedy computer, your hub for work, connection, and entertainment, has started to betray you. Simple tasks take an eternity. Programs freeze for no reason. Strange things happen that you just can’t explain.

You start to wonder, “Is this just what happens when computers get old? Or is something more sinister going on?”

It’s a common dilemma. While it’s true that computers can slow down over time, many symptoms people blame on age are actually classic warning signs of a virus or malware infection. Malicious software can run silently in the background, stealing your computer’s resources, compromising your security, and causing all sorts of chaos.

But how can you tell the difference? We’re here to help you play detective. This guide will walk you through seven of the most common warning signs of a PC infection. If you find yourself nodding along to several of these points, it’s a strong indication that your computer needs more than just a simple tune-up.

Warning Sign 1: The Sudden, Unexplained Slowdown

This is the most common symptom of all. You’re not imagining it: your computer really is slower than it used to be. But the key word here is sudden. While a PC might become slightly less snappy over several years, a malware infection can cause a dramatic and sudden drop in performance over just a few days or weeks.  

Applications that used to launch in a second now take ages to open. Saving a file results in a spinning wheel that seems to last forever. Even just moving your mouse across the screen can feel laggy and unresponsive.

Why it happens: Viruses and other types of malware are essentially unauthorized programs running on your computer. They consume your system’s resources—the processor (CPU), memory (RAM), and hard drive activity—to carry out their malicious tasks. This leaves fewer resources for your legitimate programs, causing the entire system to grind to a halt. It’s like trying to drive a car with the emergency brake permanently engaged.  

What you can check: You can get a quick look under the hood by opening the Task Manager (press Ctrl + Alt + Delete on your keyboard and select “Task Manager”). Click on the “Processes” tab and look for any programs with strange names that are using a high percentage of your CPU or Memory. If you see something you don’t recognize hogging all the power, it’s a major red flag.  

Warning Sign 2: A Plague of Pop-Ups and Unwanted Ads

Are you being bombarded with pop-up advertisements? This is one of the most annoying and obvious signs of an infection. These ads might appear when you’re browsing the internet, but a sure sign of trouble is when they appear even when your web browser is closed.  

These pop-ups are often for questionable products or services, and some can be particularly nasty. You might see fake warnings claiming your computer is infected and urging you to click a link or call a phone number for “technical support”.  

Never click on these or call the numbers provided. They are scams designed to either install more malware on your PC or trick you into paying for useless and harmful services.

Why it happens: This is typically the work of “adware,” a type of malware specifically designed to force advertising content onto your screen. It can get onto your system when you download free software that bundles the adware into the installation, or by visiting a compromised website.  

Warning Sign 3: Frequent Crashes and Mysterious Freezing

Every computer crashes occasionally. But if it’s becoming a regular occurrence, you should be concerned. Does your computer frequently freeze, forcing you to perform a hard restart by holding down the power button? Do your most-used applications unexpectedly shut down in the middle of your work?.  

Perhaps the most alarming sign is the infamous “Blue Screen of Death” (BSOD)—an error screen that appears when Windows encounters a critical problem it can’t recover from. If you’re seeing this screen more and more, it’s a strong signal that something is fundamentally wrong with your system.  

Why it happens: Malware can be poorly coded and unstable. It can conflict with your computer’s hardware, drivers, and other legitimate software. This conflict causes system instability, leading to freezes and crashes as your operating system struggles to deal with the malicious code running in the background.  

Warning Sign 4: Your Browser Has a Mind of Its Own

Your web browser is your window to the internet, and it’s a prime target for malware. If you notice any of the following changes that you didn’t make yourself, you likely have an infection :  

• Your homepage has changed: You open your browser, and instead of your usual start page (like Google), it loads a strange and unfamiliar website.
• Your search engine is different: When you type a search into the address bar, the results appear on a search engine you’ve never seen before.
• New toolbars or extensions: Your browser suddenly has new toolbars, buttons, or “extensions” cluttering the top of the screen that you never installed.
• You’re redirected to the wrong sites: You try to visit a familiar website, but your browser takes you somewhere else entirely.

Why it happens: This cluster of symptoms is the classic calling card of a “browser hijacker”. This type of malware infects your web browser and forcibly changes its settings to direct your web traffic to specific sites, often for advertising revenue or to attempt phishing attacks. It essentially seizes control of your browsing experience.  

Warning Sign 5: Strange Emails, Especially From “Yourself”

This is one of the most unsettling signs of a computer problem, as it can affect your reputation and the security of your friends and family. There are two common scenarios:

1. Your contacts receive spam from you: Your friends, family, or colleagues tell you they’ve received strange emails from your address containing suspicious links or attachments. When you check your “Sent” folder, there’s no record of these emails.
2. You receive spam from your own email address: You open your inbox to find a spam or phishing email that appears to have been sent from you, to you.

Why it happens: This doesn’t always mean your email account has been “hacked” in the traditional sense. More often, it’s a technique called “email spoofing,” where a scammer forges the “From” address to make an email look like it came from a trusted source—in this case, you. A virus on your computer may have harvested your address book and is now using it to send spam, or your machine may have become part of a “botnet” used to send out millions of spam emails. Regardless of the method, it’s a clear sign that your system or your account has been compromised and is being used for malicious purposes. This is a serious issue that requires immediate attention to protect yourself and your contacts.  

Warning Sign 6: Your Security Software Has Vanished

You were responsible. You installed an antivirus program to protect your computer. But now, when you look for it, it’s gone. Or perhaps you get a notification that your antivirus protection is “disabled,” and no matter how many times you try, it won’t turn back on. You might also notice that the Windows Firewall has been turned off without your permission.  

Why it happens: This is a tactic used by more sophisticated malware. The first thing it does after infecting a computer is to seek out and disable any security software. By neutralizing your antivirus and firewall, the malware ensures it can operate undetected and can’t be easily removed. If your digital bodyguard has suddenly been knocked out, it’s almost certain that an intruder is already inside the house.  

Warning Sign 7: Unfamiliar Programs or Missing Files

This final sign can range from confusing to downright terrifying. You might notice new icons on your desktop for programs you have no memory of installing. These are often bundled with other malicious software.  

Even more frightening is when your personal files are affected. You might go to open a document or a photo album only to find that the files are gone, have been renamed, or won’t open. In the most severe cases, you may be a victim of “ransomware,” where all your files are encrypted and you see a message demanding payment to get them back.  

Why it happens: Viruses can be designed to do almost anything, from simply installing more unwanted software to maliciously deleting or corrupting your important data. Ransomware is a particularly devastating form of malware that holds your digital life hostage. The appearance of strange programs or any interference with your personal files is an undeniable sign of a serious infection.

Conclusion: From Diagnosis to Action

If you’ve read through this list and recognized your own computer’s frustrating behavior in one or—more likely—several of these signs, you’re not imagining things. Your PC is likely infected with a virus, adware, or another form of malware.

The good news is that you’ve successfully identified the problem. These issues rarely fix themselves and often get worse over time, further slowing down your computer and putting your personal information at greater risk. Trying to remove deep-rooted infections without expert knowledge can sometimes lead to more damage. But you don’t have to deal with the frustration and security risks alone. Professional help is available to clean your system and restore it to proper working order.