I get this question all the time. “I have anti-virus software, so how did I get infected with a virus”?
Each anti-virus company has its own list of malware, which they call their “definitions”. Every company releases updated definitions regularly, usually once a day but sometimes several times a day.
Each company also has its own rules for identifying a virus that isn’t in the definitions list. If a file acts a certain way or loads itself into a certain folder, for example, your anti-virus may alert you that the file could be a virus. It also sends a message to your anti-virus company with the details about the potential new virus (the name, location and behavior). Since many of these alerts are false positives, each company has to investigate every new report before they can update the definitions.
A simple way to envision this is to imagine that every virus out there looks like a square, so your antivirus software checks every file you open or download that looks like a square. If a new virus is released that looks like a circle, it may slip through. Once the antivirus software starts looking for squares and circles, the next wave of viruses may look like a triangle, and so on. New viruses tend to stay a step or two ahead of the antivirus software.
There is usually a 24 to 72 hour window of vulnerability when a new type of threat is released. During this time, your anti-virus company must learn of the threat, perform an investigation, and then release definition updates to detect the threat.
So what can you do to help protect yourself?
There are both paid and free versions of antivirus out there, and it’s up to you which you choose to use, but make sure you do have some type of antivirus software.
Keep your antivirus updated. Most companies try to update in the hours when your computer may be turned off, so make sure you haven’t missed updates.
Check that the automatic scans are running on the schedule you have set them to run, whether it’s daily or weekly or a certain day a week.
Scan manually once in a while. Especially if you are visiting sites that would be considered higher risk- adult (xxx) sites, gambling sites, and sites where you can get pirated versions of software, movies or music are more likely to infect you than mainstream sites.
It is also important to always double check before clicking on an unknown link whether it’s on a website, private message, social networking (Facebook, Twitter, etc.) or in your email. If you are unsure whether a link is safe, copy the link and paste it into the search box at the free online link scanner.