Guide · 5 min read
How computers get viruses, and how to stop them
Malware rarely appears by magic. Learn the real ways computers get infected - email, downloads, fake updates, old software - and the habits that prevent it.
The word virus has become shorthand for any software that does something harmful: ransomware, password stealers, adware that floods the browser, or programs that quietly use your computer for someone else's purposes. Whatever the label, nearly all of it arrives through a small number of doors, and almost every one of those doors needs a person to open it.
Understanding those routes takes the mystery out of infections. This guide covers how malware actually gets onto a Windows or Mac computer, the signs that something is wrong, and the settings and everyday habits that close most of the gaps, without needing to buy expensive extra software or become a computer specialist.
From $60 + GST ($69 incl. GST) for remote help, no call-out fee
Quick checklist
- Keep Windows or macOS updates switched on
- Update the browser, Office and PDF reader
- Leave Windows Security antivirus enabled
- Download software only from official sources
- Close fake virus warnings instead of calling the number
- Remove browser extensions you do not use
- Keep a backup disconnected from the computer
Email attachments and links
Email remains the most common route. A message pretends to be an invoice, a shared document, a voicemail notification or a delivery update, and asks you to open an attachment or click through to sign in. Attachments may be Office documents that ask you to enable content, compressed files or disguised programs. Links often lead to fake Microsoft or Google sign-in pages that steal your password, which is then used to send the same trap to everyone in your address book. Hover over links to see where they really go before clicking.
Downloads from the wrong place
Searching for free software, a printer driver or a PDF converter often brings up download sites that bundle unwanted extras with the real program. Advertisements at the top of search results can impersonate well-known software and lead to modified installers. Pirated games, films and software are a reliable source of malware, because whoever cracked them has no reason to be trustworthy. The safe habit is to download only from the developer's own website or the Microsoft Store and Mac App Store, and to read each installer screen rather than clicking Next repeatedly.
Fake warnings and browser tricks
A page suddenly fills the screen saying your computer is infected, sometimes with a loud voice and a phone number. It is a web page, not a real alert, and closing the browser tab or the browser itself ends it. Other tricks include fake browser update prompts, pop-ups asking you to allow notifications, and browser extensions that promise coupons or video downloads but inject advertising or watch what you type. Only accept updates from the browser's own settings and keep extensions to the few you genuinely use.
Out-of-date software
Software flaws are discovered constantly, and updates are how they are fixed. A computer missing updates, or running an operating system that no longer receives them, can be infected simply by visiting a compromised website or by an attack across the network. Windows 10 reached the end of its standard support in October 2025, so computers still running it should be upgraded or replaced. Browsers, PDF readers, Office and Java all need updating as well, not just Windows or macOS.
Signs a computer may be infected
Malware does not always make itself obvious, and some of the most harmful kinds are designed to stay quiet while they collect passwords. Still, some symptoms are worth taking seriously. None of these prove an infection, as slow computers and odd behaviour have many causes, but several together justify a proper check before you use the computer for banking again.
- Browser home page or search engine changed on its own
- Pop-up advertisements appearing outside the browser
- Antivirus turned off and refusing to turn back on
- Friends receiving strange emails from your address
- New toolbars, extensions or programs you did not install
- Files renamed or unreadable with a ransom note
Settings that prevent most infections
Windows Security, built into Windows 10 and 11, is a capable antivirus when left switched on and updated, so most households do not need to pay for another product. Turn on automatic updates for the operating system and browser. Use a standard user account for daily work rather than an administrator account, so programs cannot install without asking. Turn on two-step verification for email, which stops a stolen password being enough on its own. Finally, keep a backup that malware cannot reach, because no protection is perfect.
When to call a technician
Book a technician if you see several of the warning signs above, if antivirus keeps finding the same threat, or if files have been encrypted. We will scan the computer with several tools, remove malware and unwanted programs, clean up the browser, check that updates and protection are working and that your email has not been compromised, and set things up so infection is less likely next time.
From $60 + GST ($69 incl. GST) for remote help, no call-out fee
Related services
Virus & Scam RemovalPop-ups, scam calls and nasty software cleaned up.Computer Health Check & Tune-upA full check of a computer's drive, updates, security, startup items, backups and cooling, with a written list of findings.Software Installation & TroubleshootingPrograms installed, licensed, updated and repaired, with junk software removed and error messages tracked down.Common questions
Do I need to pay for antivirus?
For most home users, the built-in Windows Security is enough when it is switched on and kept updated, along with sensible habits. Businesses often benefit from a managed security product that reports centrally, so someone can see if a computer has a problem.
Can I get a virus just by opening an email?
Simply reading an email is very rarely enough on an up-to-date computer. The danger comes from opening attachments, enabling content in documents or clicking links and entering your password. Keeping the computer updated closes the rare cases where viewing alone is a risk.
Is a slow computer a sign of a virus?
Sometimes, but more often slowness comes from a nearly full drive, an ageing hard disk, too many startup programs or simply older hardware. A health check looks at all of these, including malware, so you know what is actually causing it.
Will a factory reset remove viruses?
A full reset that wipes the drive and reinstalls the operating system removes almost all malware. It also removes your files and programs, so back up first and scan those files before copying them back. It is usually a last resort rather than the first step.
More guides
- Why is my computer slow? Causes and fixesA slow computer usually has a clear cause - an old hard drive, too little memory, startup clutter or malware. Here is how to find which one it is and fix it.
- Common scams in New Zealand and how to spot themFake courier texts, bogus tech support calls, invoice fraud and romance scams. How the common NZ scams work, the warning signs and what to do if targeted.
- Let a scammer into your computer? What to do nowIf a caller talked you into installing remote access software, act quickly. Steps to disconnect, protect your bank accounts and make the computer safe again.
- Can Macs get viruses?Macs are well protected but not immune. What threats affect macOS, how Apple's built-in defences work and the habits that keep a MacBook or iMac safe.
- Can't log in to your email? Common causes and fixesPassword rejected, account locked or Outlook asking again and again? The usual reasons email sign-in fails and how to get back into your mailbox safely.