As computer users, we have to be always careful when browsing the internet. Never accept any suggestions of programs installation, or install popular programs like Adobe Reader, Flash Player, or Java NOT from their original websites. Most of the time, these are traps that will install additional programs without you even know it. The most common viruses are Adware, Malware, Trojan, and Cryptolocker. Some are just annoying that will infect your computer with a bunch of popups. Others will try to steal your information!
There are good free antivirus programs that will help you keep your computer clean. Customers always tell me how surprised they are that they got a virus when they already have an antivirus program. Unfortunately, this is not enough. An anti-malware program is also beneficial.
Once the machine is infected, the cleaning process can take a few scans, or up to having to reinstall the Operating System on the machine. If this is the case, your personal information usually can be saved. Your only "homework" will be to reinstall your programs. We can also help with it. A good practice is always to back up your information to the cloud, an external device, etc.