Does it?
I can send an email from the
[email protected] it doesn't mean i've got access to Her Majesty's PC...
Seriously AFAIK the forum server shouldn't ever send out an email with that "from" (it's not valid for one thing - look at any thread subscription or birthday emails you might have from the forums) , does it tell you what IP the email originated from as that is slightly more reliable to go on than the "from" field.
It's much more likely it's a virus on someones PC that is looking at recently visited sites, or emails and creating a sender address to fool people when it sends copies of itself out.