Last updated 1 week 21 hours ago by isp-admin



What is Malware?

malware.jpgMalware is an umbrella term used to describe all forms of malicious and destructive programs designed to attack a computer or network without the user's knowledge or consent. Viruses, worms, trojan horses, adware, and spyware are all types of malware.

Malware Categories

The boundaries between the following categories are vague and shifting. Keep in mind that many pieces of malware can be categorized with more than one of the following labels. For example, a malware program may be both a virus and a trojan horse.


In conversation, "virus" has come to be a catchall term for all kinds of malicious software. However, the term technically refers to a specific form of malware that copies its own code into legitimate code on a victim's computer. When the infected legitimate code is run, the virus's code will also run, allowing the virus to copy itself into more programs or otherwise wreak havoc. Read more in our virus article.

Trojan Horses

Trojan horses (or "Trojans") are pieces of malicious software masquerading as legitimate files. Like the proverbial Trojan horse of the Aeneid, they fool the unwitting user into downloading or executing them, at which point they unleash destruction. Read more in our Trojan Horses article.


Adware sits inside a computer, barraging its user with advertisements. Obnoxious, unsolicited popup ads are an indicator of adware. Read more in our adware article.


Spyware is software that runs quietly in the background, watching the user's actions. Spyware can see when a user enters private information (such as passwords on a bank website), and may relay this information to its creator. Keyloggers are an example of spyware (see Keylogger.)You can also read more in our spyware article.

Browser Hijackers

These programs change browser settings so that users are redirected to websites they did not intend to visit. A browser hijacker may change a user's homepage, add links to a user's bookmarks, or generally cause unexpected browser behavior 1. Browser hijackers can function as adware by redirecting users to commercial sites, and are also known for bringing people to pornographic sites.


Worms are pieces of software primarily concerned with replicating themselves and spreading to many computers. Worms can slow down networks by emailing themselves to other computers in vast numbers. Worms differ from viruses in that they can duplicate themselves without user interaction 2. Read more in our worms article.

What to Do if Your Computer Is Infected

The best way to deal with malware is to avoid it from the beginning; however, that isn't always possible. To remove malware, scan your computer with your virus scanner. If you don't have a virus scanner, there are free ones available online. You can look at our wiki's list of antivirus software to get started.

Make sure that your operating system and all applications are updated. Applications such as Adobe Flash, Adobe Reader, and your virus scanner are especially important to update. This will help prevent malware infections on your computer in the future.

One characteristic of malware is that once it installs itself on your computer, it will often create backdoors for future viruses to infect your computer. When your virus scanner detects and removes a piece of malware, it often times doesn't remove the backdoors that malware creates. Sometimes it automatically reinstalls itself after having been removed by your virus scanner. One of the most reliable ways to rid your computer of malware is to reinstall your operating system and format your hard drive. Make sure you back up your data before doing this. You should be very cautious when doing this; it is not always a practical solution. Most of the time a good antivirus scanner will work.

What can Malware Do?

Some malware attacks computers, deleting files or preventing legitimate programs from running. Other malware remains incognito, carrying out tasks that computer owners are unlikely to notice, such as keylogging to record users' private information.

How to Protect Against Malware

  • Use protective software. Every computer ought to have a firewall and an antivirus program installed. Antivirus software needs to be kept up to date, as new kinds of malware are being created every day. Some antivirus programs will update themselves automatically, but others require user action.
  • Exercise strict discretion in choosing which sites to visit. Certain sites ought to immediately attract suspicion, particularly those that generate popup ads, deal with illegal activities like file sharing or pornography, or request confidential information.
  • Users can pick up malware just by visiting certain sites, regardless of whether they ever click a "download" button. For this reason, it is better to choose not to even open a site that seems potentially untrustworthy. Keep your browser (Internet Explorer, Firefox, Chrome) updated to avoid these "drive-by" browser attacks.
  • Block Javascript while using the Internet. Javascript can allow websites to invisibly place malware on a user's computer.
  • Exercise discretion in viewing email. Malware often travels the Internet packaged within electronic mail. Be very careful when downloading attachments, and absolutely never download an attachment from an unknown source. Even emails that appear to be from friends should be suspect (some malware is clever enough to package itself in a bogus email message that pretends to be from somebody whom the user knows.)
  • For more adventurous users, a system freezing program such as Deep Freeze can provide practically absolute protection against malware.

Where Can I Learn More?

Listen to our podcast about viruses and other malware here.

Click here to read ‘’Protecting Your Home from Computer Malware’’, a post by guest blogger Chris Larsen of Blue Coat.

Specific Malware