My email account has been hacked and my address book has been used to send unsolicitated emails to all my contacts, how can I stop this activity

First of all Run windows in safe mode (with network) and change your password on your email account. Then run several anti-malware programs (there are many free ones, but not all are trustworthy) Malwarebyte >> http://www.malwarebytes.org/mbam.php Microsoft Safety Scanner >> http://www.microsoft.com/security/scanner/en-us/default.aspx Windows Defender >> http://windows.microsoft.com/en-us/windows/using-defender Spybot >> http://www.safer-networking.org/en/index.html Kasperky >> http://www.kaspersky.com/security-scan Rootkit scanner TDSS-Killer >> http://support.kaspersky.com/5350 And when all is clean, change password for your email account again.