[OT] Think my PC might be pwned..?

[dogscoff]

Strangest thing... for the last few weeks I]ve been getting a hell of a lot of bounceback emails that suggest that mI've been sending out shedloads of spam. None of it seems to be from any address I actually use. Here's an example header of a mail apparently sent form my machine, or at least from my account:

Code:

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  From: "Tatum N. Florence" <cnqlad@dogscoff.plus.com>

  To: 

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recipient's address removedCode:

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  Subject: That wasn't such a surprise.



Your message cannot be delivered to the following recipients: 

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Note that I am not 'Tatum N Florence, I never use cnqlad@dogscoff.plus.com, in fact I never send anything from dogscoff.plus.com - It's all mapped to dogscoff.co.uk

This kind of indicates to me that the problem isn't on my machine- it could be either (a) someone has somehow hacked my ISP details and is logging on as me from another machine somewhere else entirely and sending email from my account or (b) they aren't using my account at all, just setting the reply-to to look like I sent them, when in fact they came from a totally unconnected address.

AVG, adaware, spybot scans come up clean. I use firefox rather than IE and keep spywareblaster up to date, so I ought to be pretty clean. Anyone know where to go or what to do find out what's going on?