(Mark Huffman @ ConsumerAffairs) There is growing concern about cyber security, especially among businesses and organizations that maintain vast networks. But consumers have to be aware of any threats to their personal computers and mobile devices. These threats are usually in the form of malware.

Malware is a general term to describe software you did not knowingly install and that disrupts the normal operation of your machine. It can simply be annoying or a serious threat. Your anti-virus software is supposed to detect and deflect these programs but, for a number of reasons, some can slip by.

Here are some signs that your PC might be compromised:

The machine runs at a slower than usual speed. We're not talking about your Internet speed, necessarily, but the speed in which your computer operates software programs and performs tasks.

If you find that your browser is taking you to a different site than the one you selected from your bookmarks, or a search engine gives you odd, unpredictable results, it's a sure sign your computer is infected with malware. After all, the main purpose of malware is to give someone else control over your machine.

Use care in downloading fixes

There are a number of free programs that will scan your system in search of malware, but be very careful, checking out any program before you download it. Michael, of Plano, Tex., downloaded MyCleanPC, which is advertised on TV, and now wishes he had not.

“Almost immediately I began noticing an unbelievable number of advertisements of all kinds on my laptop, making my laptop run even slower,” Michael wrote in a ConsumerAffairs post. “I have so far uninstalled all traces of MyCleanPC from my laptop, and the effect is spectacular. No more silly and annoying ads and my laptop is a bit faster.”

Malware is sometimes enabled by a rootkit, which is a type of software that can disguise what your computer is doing. Sometimes, it can even fool your anti-virus software. Once an attacker gains access to a compromised computer, it can perform just about any tasks you can, including changing settings.

Some may recall the 2005 scandal involving Sony BMG Music, which was accused of secretly including a rootkit in music player software that came with music CDs. The rootkit was designed to protect the copyright by limiting the consumers' access to the CD but it also amounted to a major security breach.

A nasty threat

While a rootkit is very hard to detect, it may be even harder to remove. In some cases it requires the replacement of hardware. Fortunately, rootkits are not as common as run-of-the-mill malware. In most cases, malware is used to direct your attention from what you are looking for and toward something that the attacker wants to sell.

To do this malware often attacks and changes your DNS server settings. Internet addresses are not words, like ConsumerAffairs.com, but a series of numbers, punctuated by periods. DNS servers provide the translation from the name you typed into your browser's address line to the numbers, which identify the site's real address.

Hackers have learned that if they can control a user’s DNS servers, they can control what sites the user connects to on the Internet. A malware called DNSChanger performs that task. By using malware to change the user’s DNS server settings, the criminal can force the user to go to a different site than the one the user actually wants.

Last July the FBI found and disabled a number of rogue DNS servers operated by malware hackers. As a result, the consumers whose machines were infected with DNSChanger found their machines would no longer connect to the Internet.

What to do

If you suspect your machine is infected with malware, you could troubleshoot the problem yourself, but you are probably better off seeking professional help. Seek an independent computer repair shop that has a good reputation. That will usually yield better results that using repair services operated by big box retailers.

Once your machine is cleaned and repaired, make sure you keep your anti-virus software and computer operating system updated. It's probably not a bad idea to take your computer to a repair shop for a diagnostic tune-up once a year anyway, just as you would get regular service for your car.

All this assumes you are running Windows. If you are using an Apple machine or a Chromebook or running Linux on your computer, you're most likely home free.