And viruses are only one of many threats. Some spam e-mail messages use so-called phishing schemes to trick recipients into revealing banking or credit card information. Miscreant advertisers use spurious pop-ups that exploit operating system weaknesses to hijack victims’ browsers or install spying software.

As security threats have grown to encompass more than viruses, security experts have adopted the term malware to describe all malicious code. Combating this stew of invaders requires defense in depth–multiple barriers between the malware and your system.