The problem, says F-Secure, is that there are so many layers that need to be taken into account: the operating system, web browser and third party applications and plug-ins like Adobe Reader, QuickTime and Flash.
According to F-Secure, Microsoft's automatic updates help keep the Windows operating system up to date.
Whilst the software giant releases updates on the second Tuesday of every month, it will be ending support for Windows Vista with no service packs installed on April 13, as well as ending support for Windows XP Service Pack 2 (SP2) on July 13 this year.
The end of support, says F-Secure, means that customers need to upgrade to Vista Service Pack 2 or XP Service Pack 3 in order to continue to receive security updates, fixes, or assisted support from Microsoft customer service/support.
F-Secure says that this change will affect around 10% of its customers and, as a result, it is strongly advising affected users to upgrade their machine's operating system and software.
F-Secure adds that PC users can access its free Health Check website to work out if they affected by the changes.