Goodmorning.
I suspect to be infected by a virus, becouse I am receiving lot of emails warnig that I have sent e-mail to unknown people, with this object:“ndbbz cur ukxq”.
Awast have not detected any virus how can I be sure to be clean?
Thank for your help.
Gianluca
Are you using Windows XP?
Can you schedule a boot-time scanning?
Start avast! > Right click the skin > Schedule a boot-time scanning.
Select for scanning archives.
Boot.
Then, download, install, update and run www.ewido.net 
This can also be because someone who has your email address in their address book is infected and sending out emails with your email address faked as the From: address. Dumb email servers don’t check to see if the email headers are faked and bounce it to the From address (yours).
You don’t say how many lots is, 5 a day, 10, 20, 50, etc. the more received could mean that you do have a spambot trojan on your system and should do as Tech suggests, get ewido and run a scan from safe mode.