Spyware, adware, and viruses all cause your computer to behave erratically and will usually slow it down quite a bit.
Some freely available programs can help keep your computer running worry-free of these threats.
Spyware has become a big problem for all internet users. Anyone who has access to the internet is at risk. While most Spyware is harmless, its effects can still be rather annoying and drastically slow down the performance of your PC. Spyware is a term for special codes that developers of software have created that will infest your PC for their benefit. With Spyware on your computer, these developers can track your surfing habits, monitor your online shopping preferences, and it can even alter your system files. Some of the most obvious symptoms of Spyware on your PC are slow performance, popups when you are not browsing the web, and software on your computer that you did not install.
The IT department highly recommends having some form or spyware/adware detection and removal software. A good combination of detection, prevention, and removal is MalwareBytes and Microsoft Security Essentials. Both are free and have support on the web (Note: The IT department can not assist you with these programs as they cannot work on personal computers). It is recommended that you update and run these scans regularly (even once a month is fine) to ensure that you are spyware and adware free.
Wikipedia has a good amount of information about what spyware and adware and how it affects your computer.