[header] How to remove malware [title] Understand that viruses, trojans, worms, spyware and bots are all malware that can damage your system. [substeps] A trojan is software that may look legitimate, but tricks you into downloading it. It then activates, and can delete files and steal data or give the perpetrator access to your system. 
A rootkit can be downloaded unknowingly along with other programs that you install. It can hide on your computer and can avoid normal means of detection.