There is a virus that connects itself to email.it is dormant so your antivirus will not detect it,and in time it will harm your hard drive.to check for it:
click start
choose find
choose files and folders
select find
search your c-drive
look for SULFNBK.EXE
IF FOUND,DO NOT OPEN,DELETE AND EMPTY RECYCLE BIN
click start
choose find
choose files and folders
select find
search your c-drive
look for SULFNBK.EXE
IF FOUND,DO NOT OPEN,DELETE AND EMPTY RECYCLE BIN