Malware identity theft is a problem for a lot of people in this world who use their computer. Maybe 90% of computer users have regular internet access. Their are also many jobs where it is a necessity. There are a myriad of causes that begin to slow down your computer or even cause it to begin spouting error messages at you, failing to open things you normally use and in some cases causing complete software/hardware failures.
In general accessing the internet is one of the most consistent causes as spyware/adware and malware sneaks onto your improperly protected pc. Another main culprit for your pc slowing down or having problems is the windows registry (a library of shared files for running multiple applications at the same time). The final main culprit is bad software such as free-wares. Most (but not all) freeware programs are free for a reason. It is not necessarily because they are poor programs.
I have used some outstanding freeware in the past, but they almost all contain some form of spyware/adware or even worse malware such as viruses. When you download freeware - even well known programs, you are taking a huge gamble. The problems may not even occur whilst you are using the program (aside from pop-up ad's), but when you try to uninstall the software, it will often take out some important shared files from the registry because it has been designed poorly just to get the malware onto your pc.
A very common way you can tell if you have a potential malware on your pc is to look for that program in the windows control panel section. Go to add/remove programs - if the program isn't there it is most likely malware. There are cases where it not, but it usually is. The last thing the program creator wants is for you to be able to easily uninstall their malware! Under these circumstances you will have to go into your program files, find the right folder and use the uninstaller supplied. Even with this method you cannot be sure that the uninstaller has removed everything, nor can you be sure that it hasn't damaged important files.
The problem with malware is that it is extremely sophisticated and can "piggy-back" onto your computer just while you are viewing a web page that contains it. You must never underestimate how serious of a threat malware can be to your security, one of these programs could easily be logging you credit details or log-ins as you type them into websites. Identity theft and fraud are on a massive increase through the use of the internet. The biggest problem you'll find when you do realise that you must have better protection against these attacks is; choosing the right programs to protect your privacy. There are many "fake" or "less than adequate" programs out there and it is very easy to get ripped off.