causes; 1) absent of antivirus 2)irregular update of antivirus 3)transferring of diskette in use or any other external storage devices from on system to another 4) downloading of files from the net without scanning preventions : 1)installation of competent antivirus scans 2)regular updating of antivirus programs 3)scanning of external storage devices before use 4) scanning of downloaded files from the net before accessing symptoms of virus attack 1)corruption of files [documents] 2)system hanging 3)corruption of application files 4)system restarting 5)system not coming up 6)termination of installation of system software/application. follow this tips and keep your system virus free