My first thoought was that your avatar's excessive smoking was responsible for that hacking. 

It could be someone who has you in their address book getting an infection, rather than your machine, or your address could have been harvested from Yahoo Groups posts.

Scan your system with Malwarebytes and see if it finds anything-it's effective and free...

http://www.malwarebytes.org/products/malwarebytes_free

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The Wisdom of bagginsbill:

"Oh - the manual says that? I have never read the manual - this must be why."
“I could buy better software, but then I'd have to be an artist and what's the point of that?"
"The [R'osity Forum Search] 'Default' label should actually say 'Don't Find What I'm Looking For'".
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