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Grow Your Business Security

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

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  • Viruses and malware are common and can have drastically negative results for 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.
  • There are steps you can take to remove computer viruses.

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.

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 into downloading 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.

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.

Here are six signs your computer is infected, according to Tim Armstrong, a malware researcher at Kaspersky:

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."

Plus, legitimate protection software, such as Windows Defender or various virus scanning programs, never prompt you to call a random customer service number.

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 phantom, your computer may have a virus or malware.

Your files might be missing, or the icons and/or 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.

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."

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; they have to be started by someone. And if you didn't initiate these connections in the past, problematic software could be doing it for you.

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.

Be proactive. The first step is to prevent your computer from getting infected in the first place, Armstrong said. That includes making sure your applications, antivirus software and operating system are updated.

You can also reduce the number of potential vulnerabilities that cybercriminals could exploit by uninstalling applications you don't use much.

But if your system is already infected, follow these tips from Kaspersky:

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. Next, you should install and/or run antivirus software (if the malware will let you) to fix the problem. If that's not an option, continue with one of the following steps:

Starting your computer in Safe Mode may let you run antivirus software or otherwise explore the problem. 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.

Some nasty forms of malware cripple or kill antivirus software. If that happens to you, burn a Linux-based rescue CD, which will reboot your PC or Mac and disinfect and repair its 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. Note that this step works only if your computer also has a CD drive.

Antivirus companies keep up with virus and malware trends. They often offer advice for how to deal with specific malicious programs.

The best defense is a good offense. Take the necessary precautions to keep your computer from getting infected. Install antivirus software now if you haven't already, and follow good safety and security best practices online.