Here's what you should look for when choosing anti-virus software:

Effective Virus Detection. Viruses are detected by antivirus software in two ways: a full scan of your hard drive, or in real-time as each file is accessed. It is critical that antivirus software provide both these features, especially real-time protection. Does the product quickly identify infected files with a realtime scanner, whether it comes via email, IM Apps, web browsing, etc?

There are a number of certification laboratories that test the detection rate of antivirus software, purely rating products on whether or not they are capable of detecting in-the-wild viruses. I recommend only choosing products that are certified by at least one recognised certification scheme. Check the following sites to see whether the product you're interested in passes their tests:

West Coast Checkmark http://www.westcoastlabs.org/

Virus Bulletin 100% awards http://www.virusbtn.com/index

ICSA https://www.icsalabs.com/icsa/icsahome.php

There may be several certification programs to choose from and you'll need to match the product version you're considering with the platform you intend to install it on.

Effective at Cleaning or Isolating Infected Files. Does the product thoroughly clean, delete, repair, or quarantine the infected file to stop the spread of the virus and save the rest of your system/network?

Performance and Ease of Use. No product will be effective if users do not understand how to use it, if certain features are absent, or if it has a negative impact on their system. How easy is it to install the software? How easy is it to scan for infected files? Can you schedule a time when your files will be inspected or specify what files will be inspected? Are the features easy to access and understand? Some anti-virus programs interfere with other software - in certain cases making programs unstable or worse. All anti-virus software will slow your computer down, but the best have the least impact on performance.

Ability to update. Keeping antivirus software up to date is critical; more so than with any other software. Computer viruses are being written every day. The product should be able to update easily and should allow for full customization of the types of files to be scanned. Does the software developer provide regular updates? Are they free? If so, for how long? Will the software update automatically, or does the operation have to be performed manually? Anti-virus software should provide the option to change any of these settings and to schedule the automatic updates at a specific time that suits you.

Activity reporting. You should be able to view what each demand scan found and what it did with any infected files. You should also be notified immediately of any infection found with the realtime scanner.

Support. Does the software developer provide adequate technical support (extensive frequently asked questions/knowledge base, email support, help desk phone number, etc.)?

Help Documentation. Is there a help document available? How useful is it? Is it easily understood without relying on technical jargon? Can you find your answers easily?

Check the system requirements before you buy.