The world was given a crash course on how viruses spread when the novel coronavirus COVID-19 rapidly moved across the world in 2020. Biological viruses easily can spread from person to person, but computers can be afflicted by their own types of viruses that also can spread quickly.

Stopping computer viruses involves becoming familiar with just what they are and where viruses originate. According to Malwarebytes, a cybersecurity company, a computer virus requires a host program. It then requires user action to transmit that virus from one system to another. At that point, the virus attaches a bit of its own malicious code to other files or replaces files outright with copies of itself.

While viruses and malware tend to be grouped together, some forms of malware, like computer worms, are able to spread across systems and networks on their own. That can make them even more dangerous and widespread.

Computer viruses do not generate naturally. They need to be created by programmers. These programmers may do so to steal victims’ identities, to get around restricted data, for bragging rights, or to damage organizations or competing businesses. A virus, for example, may sit undetected on your computer monitoring online usage, recording credit card information, passwords or identity information, advises Interworks, a technology company.

Most of the time viruses make entry to your computer or other device through attachments or links. Here are four common places viruses and malware lie in wait.

1. Downloaded purchases: Downloading software, games, files, and other technology from the internet is not without risk. There are many reputable sites, but unknown downloads may carry viruses.

2. Network links: More than one device hooked up to a network means any computer on that network is vulnerable should one device pick up a virus. All connected computers can be compromised by one virus.

3. Email attachments: Computer How To Guide states that emails are one of the most common ways viruses are downloaded onto computers. Opening an email from someone you don’t know can trigger malware or a virus. Never click on a link or open an attachment from an unknown sender.

4. Messaging apps: Apps that enable people to communicate through chat on desktop or mobile systems can be spreaders of viruses, too. Do not visit links posted in messaging applications unless you are sure they are from safe sites. Sometimes messenger services can be hacked, so even if links come from relatives or friends, verify those links before clicking on them.

New viruses are being created daily and computers need protection. Good anti-virus programs can help, but computer users also need to do their part to avoid contracting viruses.