Malware is a general term for the whole gamut of undesirable software programs including viruses, worms, rootkits, trojan horses, spyware, and adware.  Malware software is intentionally designed to make unauthorized and often harmful or disruptive changes to a user's computer. Malware infections can slow down your computer, make it unresponsive, unusable, cause it to crash, annoy you with pop-ups and unsolicited advertisements, or possibly steal personal and sensitive information such as passwords or credit card numbers.