12 Signs Your Computer Has a Virus

Think twice before you click on that link—even if it was sent to you by a friend or family member.

What is a computer virus?

Simply put, a computer virus is a program that you did not install which often performs malicious actions and spreads itself throughout other connected systems, explains Frank Downs, director of cybersecurity practices at ISACA. “The first computer virus was the creeper worm, in 1971. It was rather innocuous, but annoying, traveling across ARPANET and leaving little messages asking for people to catch it,” Downs says. “Over time these attacks have evolved to conduct serious damage yet are still self- propagating and still, on many levels, quite annoying.”

Robert Siciliano, Security Awareness Expert and CEO of Safr.Me adds, “Because of the intrusive nature of a computer virus, its installation needs to be covert in nature such as clicking the link in the body of an email or visiting an infected website and getting a ‘drive-by’ a virus on your device.”

The latest trend: ransomware attacks

“Ransomware is a particularly nasty practice wherein cybercriminals use a type of malicious software that blocks access to a computer system or data, usually by encrypting it, until the victim pays a significant fee to the attacker,” says Zohar Pinhasi, CEO of MonsterCloud. Instances of the attacks are surging; according to Symantec’s 2019 Internet Security Threat Report, attacks on enterprises are up 12 percent. A new business will fall victim to an attack every 14 seconds this year, according to Cybersecurity Ventures, and the attacks have generated millions of dollars for criminals. Attacks are on the rise for individuals, too. “If you find yourself the victim of a ransomware attack, seek professional help by a cybersecurity company or expert immediately,” he suggests. You should also report it to the local authorities and the FTC.

Signs that your computer may have a virus:

There are several signs, both obvious and more discreet, that you may have a problem. See the list below, and also check out these security warnings you should never ignore.

You are getting more pop-up ads than usual

“Users may notice unusual pop-ups or an increase of ads on the websites and browsers they commonly use,” says Ray Walsh Digital privacy expert at ProPrivacy.com, who notes they may be caused by adware.

You’re being automatically redirected to suspicious sites

“If you’ve typed in google.com to your address bar and suddenly find yourself on a site offering discount electronics, you can be almost certain your computer has been infected with a bug that pushes you toward certain advertisements and URLs,” cautions Pinhasi. Here’s how to tell you’re on a fake shopping site.

You can’t access your files

“One of the clearer indicators that an individual may have a computer virus is the inability to access their own system,” shares Downs. “This can result in something as innocuous as not being able to access an application on their computer because they suddenly don’t have permissions.” For example, if you regularly use a program, such as a text editor, then one day you can’t log on to it and receive notifications that you “do not have permissions” to access that tool, it could be due to a virus.

Your computer is running very slowly

“If your computer is operating a lot more slowly than usual, a virus could be the culprit,” says Walsh. That’s because many computer bugs operate around the clock in the background, so your computer is forced to do a lot more work than it typically would, he explains. If you don’t have a virus but your computer is running slowly, try these 10 tricks to help it run faster.

You have an increase in data usage

“Many unwitting members of botnets (large networks of computers which act as online armies to conduct attacks for hackers or hold their data) never know that they are part of these expansive networks,” Downs says. “However, one way they may be able to identify a potential infection is through sudden increases in data uses. If an individual receives their monthly cable or internet bill and notices that they used a much larger amount of data than they usually do, it could mean they are infected and part of a botnet.”

Your computer is making a lot of noise

A hard drive that constantly makes noise and seems overly active—even when you aren’t actually using the computer—may be a sign that someone else is using the machine, notes Walsh. Also, a PC or laptop that unexpectedly wakes up may be a sign of an infection, though it could also be due to regular Windows updates or some other legitimate process, he says. Even if you don’t have a virus, these 11 tricks will help make your laptop battery last longer.

You clicked on a phishing email

“Viruses are most commonly spread through phishing, which is a technique of sending emails designed to prey on a person’s emotions to make them click a link or open a malicious attachment,” says Kayne McGladrey IEEE member and director of security and IT for Pensar Development. “Besides running up-to-date commercial antivirus software, the easiest way to avoid viruses is to pause before acting on messages. Get a cup of coffee, or at least get up and stretch, before deciding if the email is trying to manipulate your emotions through a sense of authority (someone impersonating your boss or a police officer), a sense of urgency (because of an artificial time constraint), or scarcity (supplies are limited, act now).” These are the same psychological techniques used by con artists since time immemorial, with the only difference being that con artists had to con one person at a time. “With email, social media, and text messages, threat actors can con thousands of people. No antivirus software is perfect, but pausing before acting can stop most of today’s viruses.”

Your computer crashes a lot

An infected computer may begin to act in an erratic manner, so you may notice an increase in crashes or the computer automatically restarting of its own volition, Walsh says. You may also notice a lack of hard disk space or strange disappearances of data or programs.

You’ve installed unauthorized software and apps

“Many harmful .exe programs and softwares download automatically from the internet,” says Nooria Khan, tech expert at GigWorker. In fact, according to the internet security threat report 2018, third-party app stores had 99.9 percent of discovered mobile malware. “Only trusted anti-virus/malware developers.”

Your computer is sending messages from “you”

“If your email accounts, social media accounts, or other online services start to have problems—and you notice unusual emails or messages being sent from your accounts—this may be a sign that your computer has been infected with malware,” Walsh says. Those accounts may have been penetrated directly, but it is possible that your passwords have been lifted using a keylogger on your machine.”

You don’t have any antivirus software

“A strong firewall and up-to-date antivirus program are essential, preferably with real-time scanning capabilities are essential in order to protect your computer,” Walsh says. “In addition, users must be careful to monitor for the green lock (https) in the URL bar of their browser. Websites without the green lock are a potential hazard and could lead to infection with a virus or malware.”

You let your guard down

“Don’t use open wifi in library or coffee shops as these networks are prone to malicious attacks,” Khan says. “Run malware diagnostic scans once a week—do so at night when you aren’t using your computer. And always make sure your antivirus and operating system are up to date with the latest security patches.” You should also be aware of the 16 clear signs you’re about to be hacked.

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Joe McKinley is a regular contributor to Reader's Digest, covering cars, careers, tech and more.