Hello, I remember that when I first got it out of the box my imac would start up (or boot up) quickly. But now it starts up a little slower... Do I need to do some cleaning on my computer? I don't know how... I have heard about OnyX and using the Disk Utility but I still don't know what to do since I still don't know much about the applications that imac has or the other software like onyx. and I don't know how to use the Time Mashine IF I need to use it in order to clean my imac...? this must be a funny question but, am I safe without an antivirus on my imac thanks.