Before you purchase and install software on your PC, laptop, tablet or smartphone, here are four important areas you must consider.

Software buyers' guide: System requirements

Before you install software, check the system requirements of your chosen program.

All reputable software vendors will clearly inform you of what operating system, how much memory, and what graphics capabilities your PC will require to successfully run their product. To find out details of your own system, in Windows 7 or Windows Vista go to Computer, System Properties or Control Panel, System and Security, System. In Windows XP, go to Control Panel, System Properties. If your computer doesn't support the system requirements, it may still run the program, but it is likely to be buggy and it may slow down your PC. Crucially, you'll have no comeback if your software doesn't work properly.

It's also worth checking compatibility with any existing software you use.

In the case of smartphone and tablet apps, if you buy software from outside your chosen device's dedicated software marketplace, it's doubly important that you ensure your portable has the necessary hardware to run it. If you download an app from a pre-installed app store, you can be confident your phone or tablet can handle it.

Software buyers' guide: Better safe than sorry

There are literally millions of free and paid-for software apps vying for your attention - some are brilliant, most are okay, and a few will actively damage your system. In fact, in the majority of cases where something is wrong with a PC, a software install is to blame. Before you install anything, as well as checking the system requirements, search for expert- and user-reviews of the product in question. If a reputable site such as PC Advisor gives a program a positive review - and better yet, hosts a download - you can have a good idea that it's legitimate.

See also: PC Advisor Downloads Directory

For smartphones and tablets, utilise user ratings to assess the worthiness of any app before you install.

Regardless, before you install any software on a Windows PC, make sure your Internet security software is up to date. Run a backup of your important files and folders so that if something does go wrong you don't lose anything. Most important: make sure System Restore is running and you have a recent restore point. This way you know that you can always roll back your PC to a time before you installed your new software.

See also: How to create and manage System Restore points

Software buyers' guide: Download or DVD?

Almost all PC software these days can be purchased via download. The advantages of this are that you can purchase from your PC and install immediately, there's no bulky packaging, and in some instances the product is cheaper. But you'll need a decent web connection to download large software files, and some people prefer physical media as it means they always have a back-up and a place to store their activation codes.

If you purchase via download, you'll typically have to input an activation code once a trial version is installed. Be sure to save this code somewhere safe: then if your PC fails or you simply upgrade, you can re-install your program.

Software buyers' guide: Licensing and extras

If you purchase software, in most cases you are buying only the right to use it on a single device. Some products - security software is a good example - are more typically sold in three- or five-PC licences, as you need it to run on every device on your network. In fact, some vendors now sell antivirus etc in home licences, in which you can install and run their products on every PC you own. Similarly, Adobe allows users of its design software to utilise products on two PCs. The idea being that you can use one in the office and another at home, but never both simultaneously.

Check the licence before you purchase to ensure it is fit for your needs.

Another aspect to consider is updates. Most software requires only occasional updates to patch security holes and maintain compatibility with operating systems. But some products - PC optimisation tools and antimalware - require constant updating to be useful. In most such cases by default you purchase 12 months of updates when you buy the software. You can almost always extend this at the point of sale for less than it will cost you when your licence runs out, but for this to be worthwhile you need to be convinced that you'll still want to use the software 12 months hence.

When buying all kinds of products online, it pays to be wary of added extras. Buy a laptop, and unexpected items in the basket area may include extended warranties and delivery charges. You shouldn't experience either of those when buying software, but the nature of software licences means there are some things you should look out for. Some vendors will add on extra 'bonus' programs, increase the numbers of PCs licensed, or add additional years of support. These may be useful for you, or they may not - don't be bounced into spending more than you intended to.

Other aspects to watch out for that can increase costs at the point of sale: the addition of VAT, or the conversion of foreign currencies into Sterling.