01. virus causes automatically restart systems
02. They block task manager also
03. viruses can change automatically the screen resolution without user permission
04. They not allow to edit registry
05. They do automatically delete or currupt all exe files.
06. show duplicate error messages and screens like original windows error message even though if not error in windows.
07. they not allowed to run any setup files which can already run.
08. cannot allow to open pendrive