More than I care to mention, I am called out by clients to clean up one of the many pieces of Windows malware that has crept into their computer. Even with tools like Norton Internet Security and Microsoft Security Essentials, these items can find ways to install themselves with little or no interaction from the user.
Malwarebytes, a free, downloadable, cleanup tool is my choice when removing such infections. It works quickly and well and can restore a computer to working order in most cases. It is straightforward and simple to use. Download the app and install on your Windows PC.
When it runs for the first time it will ask to update its database of known malware. Typically I then run a Quick Scan, which is usually sufficient for most infections. After it runs it will present a list of found concerns and allows you to remove them all with one click. Often, due to the nature of Windows malware, it will also ask to reboot the computer so that it can permanently remove items which might have been locked or loaded into memory.
While Malwarebytes is free to use for the individual, it will ask if you wish to install a free trial which expands it operation to include realtime malware checking and prevention. There is no need to install this in order to use the cleanup tools. In fact, I usually only run Malwarebytes when I suspect or see direct evidence of a malware infection.
If you think your Windows PC has been infected with malware, Malwarebytes is a great place to turn for help.