#7 Firewall Killer
Firewall Killers are one of the deadliest kind of spyware out there. Firewall Killers are malware applications that are responsible for bringing down your personal computers firewall or kill your PC's firewall security, rendering your PC completely vulnerable. Firewall killer applications not just disable your PC's firewall, but also kill or disble your anti-spyware and anti-virus software that are protecting your computer. Some firewall killer applications have the capability to delete spyware and virus definitions from the anti-spyware and anti-virus definitions database; in some cases you will be able to detect a firewall killer, by just knowing that your security programs have been disabled, although some firewall killers are so advanced that they render your anti-spyware and anti-virus useless, but still manage to make them appear active, healthy and working. Then only way to get rid of such a spyware application is to use advance anti-malware software out there. Firewall killers in some instances are also often called rootkits.
#8 Flooder
Flooders are the simplest and one of the most damage causing spyware applications today. A flooder's job is to "flood" or overload the users primary networks. The flooder spyware application works by transmitting damagingly huge amounts of data to all available networks, from your PC; these networks include the internet and other local area networks your workstation or PC might be connected to. Flooders are extremely hard to remove and cause havoc, while surfing the internet, if you internet access is usage based, this will draw in a big bill.
#9 Hijacker
Another type of spyware applications, that can create a mess, are the browser hijackers.
Browser hijackers, take over or "hijack" your Internet browsers. These hijacker applications then change your browsers settings, usually starting from the homepage and default searchpage to your cookie settings. The best way to identify this threat is to check your home page, if it has been changed, not by you, then your browser has been hijacked and you are a hijacker applications victim. Internet Explorer are the worst hit browsers. These are relative easier to remove.
#10 Key Logger
A key logger is a spyware application program which has the capability of recording every keystroke pressed on the computer. The key logger spyware writes the information(key strokes captured for a particular time frame) into a log file(usually a text file). This log file is then transmitted by the key logger, at a scheduled time, to a third party, who might then used the information collected for malice. Remember a key logger records almost all keystrokes that you press, these include your passwords, chats, documents typed, account numers, etc. Your personal, financial, proprietory information is completely in at risk.
#11 Malware
Malware is a very general term, given to applications that are authored for the solitary function of causing damage to a user's computer. There's almost not difference in a virus and malware, but for the fact that unlike viruses, malware cannot self replicate. Although some malware applications are known to cause even worse, if not same, amount of damage, as compared to computer viruses.