Spam question

[johngreen]

I know that it is easy and common for the sender name on an email to be changed to anything a spammer might want without this necessarily having anything to do with the person named as the sender.

I have however recently received an email into my more generally used email account from my rarely used Yahoo email account and on looking discover that spam has been sent to the entire contacts list actually using the Yahoo account – ie the spam emails are listed in the Yahoo account ‘sent’ folder.

I am aware of no mishaps within my generally used email accounts although I suspect my details have been farmed from the computer of an acquaintance as previously rare spam has suddenly and simultaneously started appearing in my various email addresses recently.

Is such a hijacking of a Yahoo account a common event and is there a way of preventing such misuses re occurring? And are there other implications?
I have removed the entire contacts list from the email account so that even if it is so abused again, it will have no one to send to.

Thanks.

jg