How to Tell if Your Computer Has a Virus: Signs, Checks and Next Steps

Your computer has started doing things you didn't ask for: pages open by themselves, pop-ups appear, or everything feels sluggish. You want to know whether it's really a virus, or just a computer having a bad day.

How Can I Tell if My Computer Has a Virus? The Quick Answer

A virus is likely when several signs appear together or suddenly: new toolbars, a changed browser homepage, programs you never installed, or security software that has switched itself off. One odd behaviour alone proves little. To check, run a Microsoft Defender Offline scan from Windows Security.

What Are the Signs Your Computer Has a Virus?

• Pop-ups when you're not browsing. Adverts or warnings that appear on the desktop, or that keep coming back after you close them.
• Browser changes you didn't make. A new homepage or search engine, extra toolbars, or searches that redirect to unfamiliar sites.
• Unknown programs. Apps you don't remember installing, or ones that start up by themselves.
• Windows Security turned off. Protection that is disabled and won't switch back on.
• Files that have changed. Documents that won't open, have strange new extensions, or a message demanding payment to get them back.
• Friends or customers receiving odd messages from you. Emails or social media posts you didn't send.
• Constant fan noise and heavy activity while the computer is sitting idle.
• Passwords that stop working, or login alerts for accounts you haven't touched.

Is It a Virus or Something Else?

Plenty of ordinary problems look like infections, and our guide on what to do when your computer is overheating covers the most common one.

How to Check Your Computer Step by Step

1. Open Windows Security. Select Start, type Windows Security and open it. Check that Virus & threat protection shows no warnings and that real-time protection is on.
2. Run a scan. In Virus & threat protection, choose Scan options, then Microsoft Defender Antivirus (offline scan) and select Scan now. Save your work and close open files first, because the scan restarts the computer and takes around 15 minutes. Your PC will restart and scan before Windows loads, which helps find malware that hides while Windows is running.
3. Look at Protection history. In the same screen, open Protection history to see what has been found or blocked recently.
4. Check your installed apps. Go to Settings, then Apps, then Installed apps. Look for anything unfamiliar, especially programs installed around the time the trouble began.
5. Check what starts with Windows. Press Ctrl+Shift+Esc to open Task Manager, then open Startup apps (the Startup tab in Windows 10). Be cautious about disabling things you don't recognise; note them down if unsure.
6. Review your browser. In Edge or Chrome, open the extensions page and remove any you didn't add. Check the homepage, default search engine and the site notification permissions in settings.

If the scan finds something it cannot remove, or the symptoms continue after these checks, stop there and get help rather than running random cleaning tools.

How Do I Check a Mac for a Virus?

macOS has built-in malware protection (XProtect) which updates automatically, but you can still check for unwanted software.

1. Check Login Items. Open System Settings > General > Login Items & Extensions and look for items you don't recognise.
2. Review your Applications. Open the Applications folder and look for anything unfamiliar.
3. Open Activity Monitor. Look for unknown processes using heavy CPU, especially when the Mac is idle.
4. Clean up your browser. Remove any Safari or Chrome extensions you didn't add, and reset the homepage to one you choose.

What to Do Straight Away If You Think You're Infected

• Disconnect from the internet. Turn off Wi-Fi or unplug the network cable. This stops malware from sending your data out or spreading to other devices. Stay offline until the computer has been checked.
• If you see a ransom demand, don't pay it. Photograph the message, disconnect the computer and report it to the Australian Cyber Security Centre through ReportCyber at cyber.gov.au.
• Don't call numbers in pop-ups or let anyone you don't know take remote control of your computer. If you've already called or given access, report it to Scamwatch and change your passwords from another device.
• Change your passwords from a different, clean device, starting with email and banking. Our guide to locking your accounts down shows how to secure them properly.
• Don't delete files or reinstall Windows in a panic. You may destroy files you need, or evidence of what happened.
• Keep your backups disconnected. Don't plug in an external drive until the computer is checked, so any infection can't reach your backup.

How Can I Protect My Computer From a Virus?

Keep Windows and your browser updated, and leave Windows Security switched on. Use a standard account for everyday work rather than an administrator account. Be wary of unexpected attachments, links in texts and emails, and software downloaded from anywhere but the official source. Use a different password for each account, turn on two-step sign-in, and keep a backup that is not permanently plugged in. Businesses should also look at their network setup, and our computer network security service covers that side.

When to Call a Professional for Virus Removal in Melbourne

Geeks I.T. Melbourne removes viruses, spyware and malware onsite and remotely across Melbourne and its suburbs for homes and small businesses.

Call for help if:

• Windows Security won't turn on.
• Scans keep finding the same problem.
• You see a ransom message.
• You've entered passwords or bank details on a suspicious page.
• The PC holds business data.

When a machine comes to us with suspected malware, we follow these steps:

1. Work out what the PC is connected to and what it can reach, before touching anything.
2. Isolate it from the network.
3. Check what is running and what starts with Windows.
4. Run an offline or bootable scan that runs before Windows loads.
5. Review the browser, installed programs and account access.
6. Confirm your files are backed up.
7. Decide between cleaning the PC and a fresh Windows install.

Our virus, spyware and malware removal page explains the process in more detail.

Not sure whether it's a virus? Call Geeks I.T. Melbourne on 03 7057 2770 or book online and we'll work out the next step with you.