In normal use, computers become cluttered with unused data, temporary files and bits of information scattered about the disc drives. Procedures such as Disc Defragmentation and Disc Clean-up alleviate this problem. Defragmentation is usually automated in Windows7 and 8 so can be ignored, but both operations can be accessed and checked. Disc Clean-up needs to be done manually - but only occasionally.
Hardly any software is completely free of weaknesses which malware can eventually exploit. Software also becomes out of date or needs new features adding. For these reasons it is essential to keep Windows up to date and the best way to do this is to ensure it is done automatically.
Scheduling automatic updates should also ensure your Windows Firewall is always on but this can be checked within the Security drop-down inside the Action Centre which is accessed via the Systems and Security section of the Control Panel (or just search for Firewall).
Anti-virus sofware is used to protect computers against malware attack and must always be kept up to date but can never be 100% effective. For this reason it is a good idea also to regularly scan with a malware removal tool - to 'catch the ones that got away'.
Advertising 'pop-ups' are not neccessarily malware - but can be an annoying nuisance. Some pop-up ads are malicious browser extensions added when you install other free software (video recording/streaming, download-managers or PDF creators) that have adware bundled into the installation.
