It almost goes without saying that it is vitally important that you have adequate virus protection software installed and up-to-date on your PC. There are a number of free anti-virus packages available if you are on a tight budget. Windows 8 comes with Microsoft's own virus protection software already installed. This may be sufficient if all you do is browse reputable sites on the internet and send and receive emails.
Of the other free anti-virus products, all of them have paid for versions that you will be encouraged to purchase. If you choose to go down the paid for route, you will get additional functionality such as a firewall (Windows already has one built in), identity protection, email scanning and more. The actual anti-virus part of the offering whether it be the free or paid for version is the same. The decision you need to make is whether you feel you need all the additional functionality or not. It often comes down to peace of mind. Personally, I make do with Microsoft's built in offering in Windows 8.1. It is non-intrusive, doesn't unduly impact on the performance of Windows and doesn't constantly try and persuade me to subscribe to a paid for product.
Viruses, whilst more numerous than ever, pose less of a problem than in the past mainly due to advances in security software and better protection within Windows itself. If you are unfortunate enough to get one, however, they are getting much more sophisticated. One type that I have seen quite a few instances of is the so called 'ransomware' virus which locks your PC and refuses to give you access until you pay up (typically £100). The message it presents normally claims to be from some police force or other, and states it has detected you have accessed illegal (usually pornographic) websites. Some versions even use the built-in web cam if your PC has one to take a picture of you which it then displays back to you on the screen. Even if you pay the ransom, it is doubtful that your PC will be returned unharmed, if at all!
Please note that viruses are usually malicious and whilst they can in most cases be removed without too much difficulty, the damage they may already have caused may be much more of a problem to rectify. For example, one fairly recent highly publicised version of the ransomware virus encrypted the contents of important files (pictures, documents, etc). Removing this virus would not have decrypted the files.
Sometimes it can be easier and less time consuming to reset your PC to factory condition (i.e. as it was when new). I do try to avoid this at all costs where possible.
If I do feel that a factory reset is the best course of action, I will usually recommend taking your PC away and carrying out the work at home. Performing a factory reset is time consuming for the PC, but not for me as I will just start the process off and come back when each stage is complete. This works out much cheaper than if I were to carry out the task on site, since I will only charge for the time spent working on the job as opposed to the time spent at a customer's home.
Finally, a vital part of ensuring that a PC can be completely recovered following a virus attack is to ensure that regular backups of important data are taken. If a virus has destroyed your favourite family pictures, they cannot be recovered without them having been saved to another device. The simplest way to backup important files is to use Windows own built in backup tool together with an external USB hard drive. These are not very expensive and could prove to be a life (or at least a relationship) saver!