Your computer, smartphone, or tablet can become infected with a virus, malware, spyware, ransomware, or other harmful software without obvious warning. While some infections are immediately noticeable, others work quietly in the background, slowing down your device, collecting personal information, or compromising online accounts.
If you've been wondering, "How do I know if my device has a virus?", there are several common warning signs to look for. Slow performance, unexpected pop-ups, unusual account activity, unfamiliar software, and changes to browser settings can all indicate that your device may be infected.
In this guide, you'll learn eight common signs of a virus or malware infection, how to recognise them, and what you can do to protect your device and personal information.
TLDR: What You Need to Know
Malware often reveals itself through unusual behaviour. If your device suddenly starts acting differently, it's worth investigating. While a single symptom does not always mean you have a virus, several warning signs appearing together could indicate that your device has been compromised and needs attention.
- Your device becomes much slower than normal
- Pop-ups appear frequently
- Browser settings change unexpectedly
- Unknown apps or programs appear
- Battery life drops significantly
- Friends receive strange messages from your accounts
- Security software is disabled or not working properly
- Files become inaccessible, encrypted, or disappear
Table of Contents
Quick Check: Could Your Device Have a Virus?
Has your device become unusually slow despite having enough storage space?
➡️ Jump to: Your Device Suddenly Becomes Very Slow
Are you seeing pop-ups even when you're not actively browsing the web?
➡️ Jump to: Pop-Ups Appear Constantly
Has your homepage, search engine, or browser settings changed without your permission?
➡️ Jump to: Your Browser Settings Keep Changing
Have you noticed unfamiliar apps, programs, or browser extensions?
➡️ Jump to: Unknown Apps or Programs Appear
Is your battery draining much faster than normal?
➡️ Jump to: Your Battery Drains Unusually Fast
Have friends or colleagues received suspicious emails or messages from you?
➡️ Jump to: Friends Receive Strange Messages From You
Has your antivirus software stopped working or been disabled?
➡️ Jump to: Security Software Has Been Disabled
Have files disappeared, become locked, or developed unusual file extensions?
➡️ Jump to: Your Files Are Missing, Locked, or Encrypted
1. Your Device Suddenly Becomes Very Slow
One of the most common signs of malware is a noticeable drop in performance. Applications may take longer to open, websites may load slowly, and even simple tasks can become frustrating.
Malware often consumes processing power, memory, or network bandwidth while running hidden processes in the background.
Signs This Needs Attention
- Your device was previously performing well
- Programs freeze or stop responding regularly
- Startup and shutdown times are much longer than before
- Web browsing feels unusually slow
- Multiple devices on the same network are unaffected
Easy Fix
Restart your device and install any available operating system updates. Run a full scan using reputable security software and remove any threats that are detected.
If performance does not improve after scanning, investigate resource usage to identify applications consuming excessive memory or processor power.
Want to Investigate Further?
Open your device's task manager or activity monitor and review which applications are using the most resources. Unexpected activity from unfamiliar programs may warrant closer investigation.
2. Pop-Ups Appear Constantly
A sudden increase in advertisements and pop-ups can indicate adware. This type of malware is designed to display advertising, redirect web traffic, or encourage you to install additional software.
Some pop-ups are harmless advertisements, but others may attempt to trick you into downloading malicious software.
Signs This Needs Attention
- Pop-ups appear when no browser is open
- Advertisements appear on websites that normally do not display them
- New tabs open automatically
- You receive frequent security warnings from unknown sources
- Browser redirects occur regularly
Easy Fix
Run a malware scan and remove any unfamiliar software, browser extensions, or toolbars. Review recently installed applications and uninstall anything you do not recognise or no longer use. If the pop-ups persist, reset your browser settings and scan your device again.
Want to Investigate Further?
Check your browser's extension list, as adware often installs unwanted add-ons that generate advertisements or redirect browsing activity. You can also review recently installed programs to identify anything that appeared around the time the problem started.
3. Your Browser Settings Keep Changing
Malware sometimes modifies browser settings without permission. This can include changing your homepage, replacing your preferred search engine, or redirecting searches through an unfamiliar service.
These changes are often associated with browser hijackers.
Signs This Needs Attention
- Your homepage changes unexpectedly
- Searches use a different search engine
- New browser extensions appear automatically
- Searches redirect through unfamiliar websites
- Browser settings revert after you change them
Easy Fix
Reset your browser settings, remove any extensions you do not recognise, and run a full malware scan using reputable security software. If the problem started recently, uninstall any suspicious programs that were installed around the same time. Once your device is clean, restore your preferred homepage and search engine and check that the changes remain in place after restarting your browser.
Want to Investigate Further?
Review all installed browser extensions and remove anything you do not recognise or no longer use. Also check your browser's search engine, homepage, and startup page settings to make sure they have not been changed without your permission. If the settings keep reverting, scan your computer again or try a different anti-malware tool to look for potentially unwanted software that may have been missed.
4. Unknown Apps or Programs Appear
Finding software that you don't remember installing should always raise questions.
Malware can download additional programs, install browser extensions, or create unwanted system services without your knowledge.
Signs This Needs Attention
- New applications appear unexpectedly
- Unfamiliar shortcuts appear on your desktop
- New browser extensions are installed automatically
- Programs launch on startup without explanation
- Software requests unexpected permissions
Easy Fix
Review your installed applications and remove any software you do not recognise or no longer use. If you're unsure what a program does, research it before uninstalling it. It's also a good idea to run a malware scan to check whether unwanted software was installed without your knowledge.
Want to Investigate Further?
Check your startup applications and disable anything suspicious from launching automatically. You can also review your browser extensions and recently installed programs to see if anything unfamiliar appeared around the time you noticed the changes.
5. Your Battery Drains Unusually Fast
Malware running continuously in the background can significantly increase power consumption, particularly on laptops, tablets, and smartphones.
While batteries naturally degrade over time, a sudden change may indicate unwanted activity.
Signs This Needs Attention
- Battery life has dropped significantly within a short period
- The device becomes unusually warm when idle
- Fans run constantly on laptops and desktops
- Background activity remains high even when you're not using the device
- Charging takes longer than normal
Easy Fix
Review your battery usage statistics to identify apps that are consuming an unusual amount of power. Remove any suspicious or unnecessary applications and run a full malware scan. Restarting your device and installing available updates may also help resolve excessive background activity.
Want to Investigate Further?
Check which apps and processes are using the most battery power and compare usage over several days. If battery life improves after removing a particular app, that software may have been contributing to the problem.
6. Friends Receive Strange Messages From You
Cyber criminals often use compromised email, messaging, or social media accounts to spread scams and malicious links.
If people report receiving unusual messages from your accounts, treat this as a potential security incident.
Signs This Needs Attention
- Friends receive messages you never sent
- Password reset notifications appear unexpectedly
- Login alerts come from unfamiliar locations
- Social media posts appear without your knowledge
- Contacts report suspicious links from your account
Easy Fix
Change your passwords immediately and enable multi-factor authentication wherever available. Review your account sign-in history for unfamiliar devices or locations, and run a full malware scan to check whether your device has been compromised.
Want to Investigate Further?
Check whether your email address appears in known data breaches using a reputable breach-notification service. You should also review account security settings, recovery email addresses, and connected devices to make sure no unauthorised access remains.
7. Security Software Has Been Disabled
Some advanced malware attempts to disable antivirus software, firewalls, or other security tools to avoid detection.
This makes it easier for malicious activity to remain hidden.
Signs This Needs Attention
- Antivirus software will not open
- Real-time protection has been disabled
- Security warnings appear frequently
- Firewall settings change without explanation
- Security updates repeatedly fail
Easy Fix
Update your security software and run a full scan. If your antivirus cannot be re-enabled or keeps turning itself off, use a reputable malware-removal tool to perform a second scan and remove any threats that may be interfering with your protection.
Want to Investigate Further?
Check your security software's logs and recent updates to see when protection was disabled and whether any alerts were generated. You can also review your device's installed programs for anything suspicious that may be affecting your security tools.
8. Your Files Are Missing, Locked, or Encrypted
Missing files or documents that suddenly become inaccessible can indicate serious malware activity.
In some cases, ransomware encrypts files and demands payment for their recovery.
Signs This Needs Attention
- Files disappear unexpectedly
- Documents cannot be opened
- File names or extensions change
- Ransom messages appear on screen
- Shared folders become inaccessible
Easy Fix
Disconnect the device from the internet and any local networks immediately to help prevent further damage. Restore files from backups where possible and run a malware scan. If important documents or photos are affected, consider seeking professional assistance.
Want to Investigate Further?
Review your backup systems and verify when the last successful backup occurred. You should also check whether affected files have changed names, locations, or file extensions, as this can help identify whether ransomware may be involved.
The Virus Check Checklist
- Restart your device and see if the problem persists
- Run a full antivirus or anti-malware scan
- Install the latest operating system and security updates
- Remove any apps, programs, or browser extensions you don't recognise
- Check for unfamiliar user accounts or administrator privileges
- Review recently installed software and uninstall anything suspicious
- Change passwords for important accounts, especially email and banking
- Back up important files to a trusted location
- Confirm your antivirus and firewall are enabled and up to date
- Seek professional help if security warnings continue or sensitive accounts may have been compromised
If You Only Remember One Thing…
Trust your instincts. If your device suddenly starts behaving differently and you notice multiple warning signs at once, don't assume the issue will fix itself. The sooner you investigate, the better your chances of stopping malware before it causes serious damage.
What to Remember
Spotting the warning signs of a virus early can help prevent data loss, account compromise, and further infection. Not every device problem is caused by malware, but unusual behaviour should never be ignored. The sooner you identify a potential issue, the easier it is to protect your device and personal information.
- Malware often causes performance and stability problems
- Unexpected pop-ups and browser changes are common warning signs
- Unknown software should always be investigated
- Fast battery drain can indicate hidden background activity
- Strange messages sent from your accounts may signal compromise
- Security software should never disable itself without explanation
- Missing or encrypted files require immediate attention
- Regular updates and security scans help reduce risk
- Multi-factor authentication helps protect important accounts
- Backups provide protection against data loss and ransomware
Frequently Asked Questions
Can a device have a virus without showing obvious symptoms?
Yes. Some forms of malware operate quietly in the background and may only become noticeable after weeks or months. Regular security scans help detect hidden threats.
Are all slow devices infected with malware?
No. Slow performance can also be caused by insufficient storage, too many startup applications, outdated hardware, or software issues. However, malware should be considered if multiple warning signs appear together.
Can smartphones get viruses?
Smartphones can be affected by malware, although infections occur differently from traditional computer viruses. Malicious apps, unsafe downloads, and phishing attacks are common causes.
Should I pay a ransomware demand?
Paying a ransom does not guarantee that files will be recovered. Organisations such as law enforcement agencies generally discourage payment because it funds criminal activity and recovery is not assured. It may also be illegal in some jurisdictions.
Is free antivirus software good enough?
For many home users, reputable free antivirus software provides a useful level of protection. The most important factors are keeping software updated and performing regular scans.
How often should I scan my device?
Most security software performs automatic background scanning. In addition, running a full scan periodically, particularly after suspicious activity, is a sensible precaution.
What is the easiest way to prevent malware?
Keep software updated, use strong passwords, enable multi-factor authentication, avoid suspicious links and attachments, and install applications only from trusted sources.
Should I delete suspicious software immediately?
If you are confident the software is unwanted, removal is often appropriate. If you're unsure what a program does, research it first to avoid accidentally removing legitimate software.
Can malware steal my passwords?
Yes. Some forms of malware are specifically designed to capture passwords, banking details, and other sensitive information.
What should I do if I think my device is infected?
Disconnect from the internet if necessary, run a full security scan, change important passwords, enable multi-factor authentication, and restore files from backups if data has been affected.
Learn More
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