When someone asks, and they often do, "what is the one program that I must have on my computer?" and that is actually a no-brainer. If your computer is connected to the internet, and that is pretty much any computer if you are wanting to stay in touch with society. You need CARBONITE installed. Basically you can ask yourself, if you have more than $50 worth of data that you would be lost without then you should be installing Carbonite because that is what you will be paying to have piece of mind, knowing that no matter what happens to your computer (fire, flood or just a hard drive crash) you are safe!
Of course you need to have antivirus (yes even Mac computers are now getting viruses). The routine maintenance and scanning of your computer for viruses, malware, spyware, scam ware and whatever else you might want to call those 'negative items' that you must deal with on a day to day basis as a result of using that information highway. Since the early days of the internet we used to pay for an annual subscription to such programs like Norton Antivirus. Although you can get these today, I am of firm believer in the open source market and paying for value products and that is why in the case of AVAST antivirus, they do offer a pro version which offers more services. Therfore one way of looking at this is the money you used to pay for annual antivirus subscriptions in the hopes that your system doesn't get a virus that renders your data irretrievable is now being spent on placing your data in your own safe deposit box in the sky (or the cloud if you want to use the currently used marketing name Microsoft and other use to give a name to a service that allows you remote storage and access. Therefore the number one item is still Carbonite in my opinion with Antivirus being the second most important for any computer that accesses a network.
Much like the LOGMEIN remote software program which I currently use for all of those that require me to help them out. Since most people that own one computer such as a desktop are now using an additional product to access the internet such as laptop, netbook, tablet or smartphone.
These are just the top three items I believe every computer is required to have. Check out my TIPS and SOFTWARE SUPPORT pages for many other software programs and help, not to mention if you find yourself reading a tip that is outdated, as much as I do try to stay current, some of my tips may refer back to the earlier operating systems or quite simply, it has yet to move to the ARCHIVES.