Lately I have experienced that my web home page changes without my authorization, prompting me to sign in, over and over again. I have gone into Preferences to choose my preferred settings. The changes are usually stable, as long as the computer is runnin. When I turn it off, or close the web, my home page is not accessible the next time unless I sign in, again. I use Safari with My Yahoo as my home page. My computer also runs slower and hesitates when changing pages. I had no problems until I allowed other users, with limited permissions, to use this comuter.