Computer programs with the purpose of searching a computer's files for computer viruses and removing those viruses are referred to as antivirus software. There are many different types of antivirus software programs that are optimized for different purposes and different types of electronic devices. Some types, for instance, are constantly running in the background with the goal of identifying and removing any file containing a virus before it has a chance to do any damage. Others are intended to periodically search through all of a computer's files for viruses on a schedule set by the user, without running nonstop in the background. Additionally, some types of antivirus software programs are designed specifically for certain computer operating systems while others are optimized for computer networks or mobile devices.
One of the major differences between various types of antivirus software is cost. Many types operate on a subscription basis and require users to pay a monthly or yearly fee to keep receiving updates. Others are completely free but do not guarantee that updates will be as regular or as reliable. Regardless, they usually perform comparably and are generally sufficient for the causal computer user. The frequent updates provided by subscription-based services are often suitable for use by businesses that need to be particularly careful about protecting and preserving the data stored on their computer systems.
Some types of antivirus software programs are cloud based while others are stored entirely on the local computer system. Cloud-based systems store the majority of the information needed to scan a computer for viruses on an external server. If a virus disable's a computer's access to the Internet, however, these types of antivirus software programs are not particularly useful. Antivirus programs that are stored on a computer's local hard drive do not have this issue, but they take up more space on the hard drive and must be manually updated on a regular basis to keep up with new viral threats.
A few specific computer viruses can be particularly difficult to remove, so some types of antivirus software programs are highly specialized to neutralize such computer threats. In general, it is necessary to install such software after infection by specialized viruses. These types of antivirus software programs can then run the processes necessary to remove the virus. The primary difficulty with such programs is that many of the more malicious viruses make it very difficult to install new software while the virus is active.