One question I’m often asked is 'Where did the virus come from?'

Unfortunately, tracking malware back to its source is often impossible. But one thing is becoming increasingly clear: the majority of malware infections do not come from the places most people think they do.

High-risk Internet behavior can lead to malware infections. File sharing services, strange emails with random weblinks, illegal pharmaceutical sites, porn sites, and sites selling things at suspiciously reduced prices (or giving those items away) are potential vectors for malware.

A good rule of thumb is - the freer something is on the Internet, the more likely there’s a catch. With free software and Internet apps, that catch may very well be spyware, adware, or viruses installed on your computer.

According to the 2013 Cisco Annual Security Report, “web malware encounters are typically not the by-product of ‘bad’ sites in today’s threat landscape. Web malware encounters occur everywhere people visit on the  Internet — including the most legitimate of websites they visit frequently, even for business purposes.”

According to that same report, 18.3 percent of malware infections come from Dynamic Content pages (like social media) and Content Delivery Networks; 16.81 percent from advertisements; 11 percent from Games and Search Engines; and 8 percent from Business & Industry websites.

Of those, only Content Delivery Networks (like Bittorrent or Limewire) would fall into the traditional “high-risk” type of activity.

How does a “good” website get infected? How can a virus infect a computer from an advertisement? If malicious code gets injected into a website (usually without the site owner’s knowledge), then every time someone visits that site, the malicious code will be run on the computer.

Similarly, every time an infected advertisement displays, malignant code can execute. Sometimes these infections occur silently, sometimes they result in pop-ups that users inadvertently grant access to their computers.

Once the code runs, it takes a fraction of a second for the system to be compromised, and that single piece of malware may then open the door for hundreds of others.

How can users prevent these problems? Short of not using the Internet, there’s no 100 percent effective solution. Use a reliable, up-to-date antivirus program.

Be careful what you click on and what you agree to install. Most importantly, if you think you’re infected, have your system examined by a reliable IT professional immediately. If caught early, malware infections can be relatively simple to repair.

If allowed to spread throughout a system, a virus can cause significant performance issues, irreparable damage or data loss and may even use your computer to infect others.