How to Tell If Your Computer Has a Virus (And What To Do About It)
Something feels off with your computer — it's running slow, there are weird pop-ups, or programs you don't recognize have appeared. You might have a virus. Here's how to know for sure, how it probably got there, and what to do next.
Warning Signs Your PC Is Infected
Sluggish performance is the most common early sign — if your computer is suddenly much slower than usual and nothing obvious has changed, something might be consuming resources in the background. Check your Task Manager: if you see a process using 50-90% of your CPU and you don't recognize what it is, that's a red flag. Malware often runs constant background processes for things like cryptocurrency mining or sending spam.
Other warning signs include browser pop-ups appearing even when you're not browsing, your homepage or default search engine changing without your input, programs you didn't install appearing in your app list, files disappearing or being renamed, and your antivirus tool being disabled or unable to update. If your computer is also generating a lot of outbound network traffic when you're not actively using the internet, that can indicate malware communicating with an external server.
How Viruses and Malware Actually Get In
Email attachments remain the single most common delivery mechanism. A realistic-looking invoice, shipping notification, or HR document arrives, someone opens the attached file, and malicious code executes. Modern attacks often use Office documents with macros, PDFs with embedded exploits, or zipped executables. You don't always need to “run” a file for it to do damage — some exploits trigger just from opening a file in a vulnerable application.
Malicious downloads are the next big one — software cracked versions, free tools from sketchy sites, or fake software updates that pop up while browsing. USB drives can carry malware that auto-executes when plugged in, which is why you should never plug in a USB drive you found lying around (yes, attackers actually do this). Visiting compromised websites can also deliver malware through browser exploits, though this is less common with modern, updated browsers.
What NOT to Do
If a pop-up tells you that your computer is infected and you need to call a number or download their software to fix it — do not do either of those things. This is a scam called “scareware” or “tech support fraud,” and it's extremely common. The pop-up itself is the attack. Calling the number connects you to fraudsters who will either ask for remote access to your machine (and then steal data or install real malware) or charge you hundreds of dollars for fake services.
Also avoid trying to remove malware by just deleting files you don't recognize or running a random “fix” tool you found in a forum. Modern malware is persistent — it reinstalls itself, hides in system directories, and modifies registry keys. Amateur removal attempts often just hide the symptoms while leaving the infection intact. Get your IT team involved or contact a professional.
What To Do Immediately If You Suspect Infection
Disconnect the machine from the network first — pull the ethernet cable or turn off Wi-Fi. This prevents potential malware from spreading to other devices or continuing to communicate with attacker-controlled servers. Don't shut the machine down completely yet if you can avoid it, because some forensic evidence exists only in memory.
Call your IT support team or contact a professional who can run proper malware analysis. For business devices, this is especially important because an infected workstation could be the entry point for a larger network compromise. Your managed IT provider should have an incident response process for exactly this situation. Don't use the infected machine for any business activities, banking, or anything that involves entering credentials until it's been cleaned and verified.
Why Modern Endpoint Protection Is Different From Old Antivirus
Traditional antivirus software works by checking files against a database of known malware signatures. This works fine for well-known threats, but attackers routinely modify their malware slightly to evade signature-based detection. Modern Endpoint Detection and Response (EDR) tools take a completely different approach — they watch for malicious behavior patterns rather than just matching signatures.
An EDR tool can catch ransomware the moment it starts encrypting files, stop a trojan the moment it tries to establish an external connection, and flag suspicious PowerShell commands that suggest someone is trying to move laterally through your network. For businesses, EDR is now the baseline expectation for endpoint security. Our cybersecurity team can evaluate your current endpoint protection and upgrade you to something that actually catches modern threats. Get in touch if you're not sure what you have or how well it's working.
Nazar Loshniv
Founder, Powerful IT Systems · Sussex, WI
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