This happened to someone i know once, they opened an email that contained a virus this then carried on sending emails from there account, the only way to stop that is clear out your inbox / outbox and change your password & also create a security question and supply your mobile number
sorry if someone else has replied with the same response i didnt read all of them so yeah sorry
btw this is where hotmail never disappoints....gmail and yahoo though more user friendly and generally better but such cases of hacked accounts also go side by side...hence moving to hotmail wont be such a bad idea if you have those occasional mails
Yeah right I agree with you. Hotmail is much more secure than gmail and yahoo. Many people above have mentioned how to recover your mail so I don't need to tell you that. If we are using Gmail or Yahoo account it is always mandatory to change our passwords timely.