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How to Tell if Your Computer Is Infected and How to Fix It

Andrew Martins
Andrew Martins

Computers infected with viruses or malware pose a risk to your privacy and security. Find out how to fight back.

  • Viruses and malware are common and can have drastically negative results on your computer and life.
  • You can often tell that your computer is infected because it acts weird or slow.
  • Active antivirus software is a good way to prevent these problems.
  • This article is for small business owners who are concerned their systems may be infected and want to properly address the issue.

Is your computer acting weird? Are boxes popping up on your screen, telling you your computer is infected? Are you hearing strange sounds? Your computer may have been infected with malware or a virus.

It's not always easy to determine whether your computer has become infected with a virus, worm, Trojan or spyware; authors of malicious software do their best to disguise their work. However, you can look out for certain signs that your computer is infected.

The negative impact of a computer infection

A virus or malware always has a negative impact, but the degree of that impact depends on the type and scope of the infection. Here are some of the possible consequences of a computer infection:

  • Loss of performance. Malware can make your computer process things more slowly. That means it may take increasingly longer for you to get work done or just look up a quick fact.

  • Loss of functionality. In extreme cases, the virus can degrade your computer performance or programming so badly that you can no longer use your machine.

  • Exposure to other negative software. The purpose of some malware is to entice you to download even more dangerous software.

  • Loss of information. Viruses might delete stored files or data.

  • Breach of privacy. In some cases, viruses seek to gather personal information about you for the purpose of identity theft or fraud. This can result in financial losses if your accounts are breached.

Key takeaway: A computer infection can cripple your operations with a loss of performance, functionality and information. It can also result in a breach of privacy and exposure to other negative software. 

Types of computer infections

According to cybersecurity company Kaspersky, things you don't want on your computer include viruses and all types of malware and spyware. Here are some common threats:

  • Viruses designed to attack your system. They spread from machine to machine via shared links and uploaded and downloaded files. People spread these programs when they link and share carelessly and don't use the right antivirus protection.

  • Worms, which are similar to viruses. These programs don't need help from people to spread. They're programmed to move across computer networks on their own.

  • Adware, spyware and ransomware. These programs are designed to track what you do online, gather data about you, and even steal your data and hold it hostage.

Key takeaway: Several different types of malware and spyware can cause significant damage to your system, including viruses, worms, adware and ransomware.

Signs your computer is infected

Here are six signs your computer is infected, according to Tim Armstrong, senior sales engineer at SecurityScorecard:

Unexpected pop-up windows

Unexpected or unusual dialog boxes and windows can be a bad sign. Fake virus warnings say you have security threats on your computer, and they usually prompt you to click a link or call a number.

"One of the things we always tell people is that, as of right now, there's no way a website can tell you if your computer is infected," Armstrong said. "Sometimes, Skype will pop up a message saying, 'Urgent security vulnerability.' But Skype can't tell if your computer is infected."

Legitimate protection software, such as Windows Defender and various virus-scanning programs, will never prompt you to call a random customer service number.

Random sounds

Infected computers are often programmed to respond with an audio signal to things you cannot control.

"They'll be things like warning beeps," Armstrong said. "When an error message pops up, a lot of times, it comes along with a warning message. Certain pieces of malware stifle that window so you can't see it. But you might still hear the warning message – a sound in the background that you didn't initiate."

If you're regularly hearing chimes and bells from your computer that seem to be phantom, your computer may have a virus or malware.

Unexplained file or folder changes

Your files might be missing, or the icons and content of your files may be different. Your computer won't make these types of changes to your files unless you have a virus or technical problem.

Slow operation

Pay attention to whether your computer is running more slowly than usual.

"One of the popular scams right now is something called 'pay per install,'" Armstrong said. "There are third-party companies out there in places like Russia and China that allow [someone] to go to their forums and sign up to receive a piece of software. They then pay [that person] for every thousand users they can fool into installing the software.

"So, these people who try to trick you into installing rogue software will put as many things on your computer as possible at the same time to make the most money," he added. "And with all this spyware and applications running at the same time, you'll see a slowdown in performance."

Random connections to unknown websites

Another sign of an infection is when your legitimate antivirus software alerts you that an application is trying to connect to a website you've never heard of.

In general, your computer doesn't make its own connections; someone has to initiate them. If you didn't initiate these connections, problematic software could be doing it for you.

Unexpected images

You might see pornographic images pop up or replace benign images, such as photos on news sites. A related sign that your computer is infected is the constant appearance of pop-up ads for sites you don't normally visit.

Inability to download antivirus programs or updates

Computer viruses aren't living things, but some are programmed to have a self-preservation instinct. For the average computer user, the No. 1 way to kill a virus is through a scan by antivirus software. If you're having trouble downloading and installing the software, or you're unable to update your existing program, that might be by the virus's design. Though this can be a hassle, some antivirus software solutions can create rescue disks to scan and clean an infected PC.

Spam sent from your email address or social media

Malware can work in many different ways. One method that's grown more common with the proliferation of email messaging and social media is a brand of malware that sends random messages to your contacts list. This sort of infection spreads across the internet by tricking people to click on an infected link. The link then spreads the malware to that person, who unwittingly spreads it throughout their friend list. By logging out of your accounts, creating strong new passwords and implementing security measures like two-factor authentication, you can thwart any further intrusion.

Sudden lack of hard drive space

Have you suddenly run out of space on your hard drive? Self-replicating viruses or worms, often called "disk bombs," can wreak all kinds of havoc on a computer system by rapidly filling hard drives with copies of itself. In many cases, the files it injects into a hard drive are invisible under default file-browsing settings.

Strange running processes

If you're a little more tech savvy than the average user, you likely know your way around the Windows Task Manager. From time to time, if your computer is acting strangely or not running as smoothly as you'd expect, it may behoove you to check the Windows Task Manager for any rogue processes running in the background. If a process name closely resembles a legit Windows process but doesn't add up, you may be infected.

Key takeaway: Viruses and general malware tend to force computers to act abnormally. If you're witnessing unusual behavior from your computer, it may be infected. Some specific signs are unexpected pop-up windows, strange sounds, unknown processes running in the background and slower operations than normal.

How to deal with computer viruses and malware

When it comes to preventing computer viruses or malware infections, you should always be proactive. The following best practices are just some ways you can work to make sure your computer remains free of malware and viruses.

Maintain your installed programs.

One of the main ways viruses gain access to a system is through security lapses in existing software. Therefore, as the first step to prevent your computer from getting infected in the first place, you should make sure your applications, antivirus software and operating system are up to date. This is doubly important when it comes to your operating system, since Apple, Microsoft and other providers regularly release security patches to deal with potential weaknesses. You can also reduce the number of potential vulnerabilities for cybercriminals to exploit by uninstalling applications you don't use.

Only install one antivirus solution.

It may seem wise to have multiple layers of antivirus protection on your computer, but this is a case of "less is more." If you have more than one antivirus software program installed on your machine, you run the risk of them canceling each other out because each thinks the other is a virus. This can result in limited antivirus protection at best, file corruption at worst.

Automate virus scans.

You don't always have to be beside your computer when it conducts a virus scan. Most modern antivirus software has automation features that let you set a specific time for the computer to conduct its virus scan. By setting the process for a time where you don't need to use the computer – like when you're sleeping – you can make sure your system is safe without it hindering your productivity.

Pop those pop-ups.

If you're dealing with rogue pop-ups on your computer, you can take these steps to address them, according to Kaspersky:

  1. Go into the Task Manager and stop the process that's running the pop-up.
    • Windows users can hit the Ctrl, Alt and Delete keys at the same time to find the Task Manager quickly.
    • Mac users can go to the Apple menu on the top left and select Force Quit to find it.
    • Note that this doesn't remove the infection.
  1. Next, you should install and/or run antivirus software to fix the problem, if possible.

Restart your computer in safe mode.

Starting your computer in safe mode gives you a chance to run your antivirus software and take a closer look at what the issue may be. Begin by rebooting the computer. On a Windows PC, press and hold F8 as soon as the reboot begins. Then, choose safe mode from the menu that appears. On a Mac, hold down the Shift key while rebooting. Then, perform an antivirus scan to eliminate any other potential infections.

Boot from a rescue CD.

Some types of malware can destroy antivirus software. When that happens, you can create a Linux-based rescue CD to reboot your computer. It will disinfect and repair corrupted files. Most major antivirus software makers offer the files for free; all you need is access to another PC with a broadband connection and a CD burner. Without a CD drive, this option won't work for you.  

Check your antivirus vendor's website.

Antivirus companies keep up with virus and malware trends. They often offer advice on how to deal with specific malicious programs in educational materials on their websites.

Take action depending on the malware you have.

Multiple types of malware can cause major problems for any machine. If you can identify what you're dealing with, whether it's ransomware or crimeware, you may be able to take specific steps to foil the program. For example, Norton suggests disconnecting from the internet immediately if you believe you've fallen prey to crimeware.

Key takeaway: There are many ways you can respond to a virus or malware infection on your computer system. By acting calmly and quickly, you could reduce the risks and damage a computer virus or piece of malware can cause.

Source interviews were conducted for a previous version of this article.

Image Credit: PRImageFactory / Getty Images
Andrew Martins
Andrew Martins,
Business News Daily Writer
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I am a former newspaper editor who has transitioned to strictly cover the business world for business.com and Business News Daily. I am a four-time New Jersey Press Award winner and prior to joining my current team, I was the editor of six weekly newspapers that covered multiple counties in the state.