Organized cybercrime is now fully engaged in the creation of spyware/malware. Programs that sit on your computer watching for specific actions like Username / Password combinations. Unbelievably, these gangs are now fighting their wars on your computer! For example there is a new piece of malware out there called Downloader.Lunii. When a user fires it up, it attempts to delete processes and files of popular adware programs like Powerscan and BargainBuddy. In other words it appears to be doing you a big favour!
The problem is that little Lunii is not so friendly as it may seem. Just like other trojans, it also changes Windows configs and tries to download files from a remote server. Trojans as a category do not try and replicate themselves from one machine to another, but sit there quietly in the background, do their best to invisible and, when called upon, provide a backdoor into your computer / network / domains.