Hi. The screensaver for my mac changed by itself for the second time. I have not made any changes. No one else has access to the Mac. Could this be due to spyware? I have installed Parallels on the Mac so I could use Windows based spreadsheets but I also installed Microsoft Security Essentials and limit the amount of time that Internet Explorer is running. No one else has access to the Mac although it is in a network with another computer (PC) that is used by several different people depending on the time of year. That particular PC, by the way, has been compromised but the Mac seemed fine until now. Should I be worried?