Help! - Subject changed in email sent from Yahoo account

Hi

 

Hope someone out there can solve a mystery for me.

 

I replied to an email from a relative, so it should have had "re: Whatever the subject was in their email" as the subject in mine, right! But when I go back to look at the email I sent in my sent box it has a completely different, malicious and irrelevant subject that I know I didn't put in there.

 

I figured there were two possibilities. Virus or someone hacked my Yahoo account, with virus being the mostly likely option.

 

I have Norton on the computer I sent the email from, so was hoping someone out there can shed light on what caused this and/or advise me what I should do about it.

 

Thanks

g