An antivirus program is software that loads automatically when you boot, then stays in the background. It protects you from Trojans, worms, spyware, rootkits, and all sorts of malware. Bvs1216 uses Microsoft Security Essentials. He asked the Answer Line forum if he needs to supplement it for additional protection. But no software is perfect, so it’s a good idea every week or two to scan for malware with another program. You need an on-demand malware scanner.”]