Malware is a class of software that is written with the intent to infiltrate computers without the users’ consent. The effects of such programs vary according to the specific type of malware that has infected the computer. The most prevalent forms of malware include computer viruses, worms, adware, and spyware.

Because most malware is written to infect Windows computers specifically, it rarely poses a threat to Mac computers. However, as malware evolves, it is a good practice for Mac users to update their virus definitions and scan their computers routinely.

Viruses and Worms


A computer virus is a small program written to alter the way a computer operates, without the permission or knowledge of the user. 

A virus must meet two criteria:

  • It must execute itself. It often places its own code in the path of execution of another program.
  • It must replicate itself. For example, it may replace other executable files with a copy of the virus infected file. Viruses can infect desktop computers and network servers alike.

Some viruses are programmed to damage the computer by damaging programs, deleting files, or reformatting the hard disk. Others are not designed to do any damage, but simply to replicate themselves and make their presence known by presenting text, video, and audio messages. Even these benign viruses can create problems for the computer user. They typically take up computer memory used by legitimate programs. As a result, they often cause erratic behavior and can result in system crashes. In addition, many viruses are bug-ridden, and these bugs may lead to system crashes and data loss.

A worm is similar to a virus except that it does not require a “host file” to transfer itself from one computer to another. Worms propagate through network connections and are most commonly transmitted via e-mail.

Adware is software that automatically displays advertising material, and is characterized by annoying pop-ups banners and unwanted search bars that have been installed into the browser.

Spyware is software that runs discreetly in the background and tracks and transmits data about the user’s computer activity. The danger of spyware is that it can steal private information from your computer, such as credit card numbers and passwords, and send the information to another site.