Since my posting, I have found a possible cause. I had problems with Kaspersky Internet security and uninstalled it with Revo after the Windows uninstaller did not do a complete job. I then reinstalled MSoft Security Essentials. However Kaspersky has now shown itself as running with an icon in the task bar. It does not show in list of programs installed in the program list on Windows, neither does it show as installed in CCleaner or Revo but it is running ! Any ideas as to how I can get rid of this ?