How is someone sending email from my computer?

I went to check my mail and saw all these failure delivery things. I didnt send these emails, and dont know who is. How do I stop someone who I dont know from sending emails from my computer? How are they doing this? UUUGggg Im confused!!!! Didnt know this could happen. I have that spy sweeper program, so I don't think it is spyware, but I dont know much about computers so....got me.

Someone please help me!!!!

[edit on 12-6-2005 by mrsdudara]

Someone could have been using your e-mail address without directly using your computer.

sometimes that means you have some sort of virus or trojan on your computer
try running a scan

Originally posted by worldwatcher
sometimes that means you have some sort of virus or trojan on your computer
try running a scan

The program is set to run a scan every time I start up my computer. So far it has not found anything. I will try it again though.

thanks

MrsD, I found these, maybe they can help isolate the problem
www.olympus.net...

service1.symantec.com...

hope it helps

I had the exact same problem. I notified my ISP about what was going on and I havent had one since. My email was hijacked by pornspammers and my isp apparently tracked them down and put a stop to it.