After giving it some thought,I believe a hacked account or a virus is not the case here.
If the spam emails are not in your sent folder,then this is what might be the culprit.
Yesterday,I was talking to a friend about automatic promotion via e-mail of whatever using bots.
Now we "created" a (hypothetically) working bot that using a complex algorithm , sends spam e-mails to random accounts.
Using a loop and a mail function you can basically send e-mails to anyone from anyone.This of course is all computer generated,and the reciever can not tell the difference , if a human wrote it or machine.That leads to an assumption,that the said user (Tanya) in this case and many others are sending spam e-mails.
Basically using arrays with random words,letters and numbers (abiding by e-mail name rules-meaning no #,$,% in names,etc.)
,attached together randomly in many variations.You can also throw in some googled email adresses(just a thought) by treating the search page as a string and extracting what's needed with some relatively easy to use functions.
That way,the person writing the bot can do whatever he wants with minimal effort.
Now another theory is that in this forum somebody is messing with the e-mails of others.How?Well I noticed that next to the profile button theres an email button for those who added it in their account details.That way using the same method above,but without an algorithm , rather just your e-mail and some other random user's , the same thing can happen.
I'm sorry if I bored you people with this,it's just some thoughts and observations.
However I encourage you to change your password and see if that works out for you 
P.S - This is not perfectly thought out and some parts may seem illogical.I'm very tired,but I hope you get the genaral idea.
