“We worried for decades about WMDs – Weapons of Mass Destruction. Now it is time to worry about a new kind of WMDs – Weapons of Mass Disruption.”
― John Mariotti


Malware refers to any kind of malicious software designed to damage or harm a computer system.

Malware aims to go unnoticed — to gain access to your computer without you knowing it’s there. It’s generally used:

  • to get access to, and control of, a computer system
  • for profit
  • to steal sensitive information from an individual or business
  • to blackmail someone. 

Common types of Malware

Viruses may enter your computer system when you download an infected file or visit an untrustworthy website. They’re usually attached to files you:

  • get in an email
  • download from the internet
  • get on a portable drive, like a USB drive.

When a virus gets into your computer it can spread through your programs and files, corrupting them and causing your computer to either slow down or even stop working altogether. Having a virus in your computer system can make it more vulnerable to other attacks, like ransomware.

Worms are a kind of malware that can enter your computer system through:

  • a network like the internet
  • your local network
  • portable media like USB drives.

Just like a parasite, a worm requires the host — in this case, your computer — to be operating to spread. Once they’re in your system they can move quickly and easily through lots of computers on a network, whether it’s a local network (LAN) or a global network (WAN). Worms can also damage your files and programs, and leave you vulnerable to other forms of attack.

Trojans are another type of malware. Just like the Trojan horse of Troy, they hide inside legitimate objects — for example, files like Word documents or PDFs — until someone opens them. When they get into your system, they can give others access to your computer without your knowledge. If other people get access to your computer they can download more malware, like worms, from the internet. Trojans themselves don’t spread over networks, but the other malware they download can.

Spyware and adware work by passing information to third parties about your behaviour online. This allows them to target you with advertising for products and services, whether you’re interested in them or not. Some of this content can be offensive, which can indicate that you have spyware or adware on your computer.

Adware monitors the websites you visit and pushes ads onto your device. It can choose ads that you’re likely to click on, or ads that would embarrass you. These ads can appear within a site or as popup windows. Adware can cause problems when:

  • popup windows become difficult to dismiss or close
  • information is gathered and passed on to others without asking for your consent
  • it slows your internet browser or computer down.
  • it contains objectionable material.

Spyware gathers information about the system it infects. It:

  • tracks your activity
  • monitors the websites you visit, and
  • passes this information to others outside your system.

It can even track the information you type into websites. In some cases, this means that personal or sensitive information — like your internet banking details — can be accessed and used without your knowledge or consent. This is called keylogging.

Preventing Malware

Malware’s easier to avoid than it is to fix. Here’s what you can do to reduce the likelihood of an infection.

  • Always update your operating system and your apps when new versions are available. You can set this up to happen automatically with Windows and a lot of other applications like Office.
  • Install antivirus software on your computer if you don’t already have it, and update it regularly.
  • Scan for viruses regularly and clean up any infections straight away.
  • Install a firewall on your computer to stop traffic from untrustworthy sources coming into your computer.
  • Be careful when sharing portable devices like USBs.
  • Don’t click on web links sent by someone you don’t know, or that seem out of character for someone you do know. If you’re not sure about something, contact the person you think might have sent it to check first.
  • Be cautious when connecting your computer to untrusted networks like free WiFi or internet cafés.
  • Make sure you back up your files regularly. This includes the files on your computers, phones and any other devices you have. You can:
    • do an ‘offline’ or ‘cold’ backup. Back up the data to an external hard drive and then remove the hard drive from your device — if you leave it plugged in it could become infected too
    • do a cloud backup to Dropbox or a similar online hosting service. 

If you’re affected by Malware

If you think your computer’s infected with malware, talk to your IT support person or a local computer services company. They can:

  • diagnose malware on your computer
  • get rid of it for you
  • restore your system
  • advise you on security
  • install security protection for you
  • show you how to keep your systems up to date.

There are a lot of free antivirus, antispam and antispyware products on the market. Not all of them are legitimate though, so it’s important to discuss your options with an IT professional before installing one on your computer yourself. They can help you work out what product’s best for your needs. While there’s no foolproof way to prevent malware infections, these products will help protect your computer system from them.

Visit CERT NZ for more information. 
Visit ACSC for more information.