Unscrupulous individuals use programs to "scan the web" for valid email addresses which contain an at sign and period. In many cases they'll get them from discussion boards, or even the source code of the web page (such as the destination address from a feedback form).
I maintain several web pages for some of my clients (the "other" job) and have recently become the victim of this. I get about 10-30 viri per day, all because of the feedback form addresses. I had to re-do our forms so the actual email address is no longer there and is referenced only by an ALIAS. The alias is passed to the CGI/perl (program that runs on the server), which knows and hides the real address. Whoever is doing this seems to be doing it on a LARGE scale.
Messages tend to have a virus or trojan attached, with subjects such as "A special funny game", "to class", "Worm klez.e immunity", "w32.klez.e removal ools", "hyperlink", "onmouseout", "Spice girls vocal concert", "a good tool", "A winXP patch", "a funny website", "your password", "to revise the hip", "Let's be friends", "privacy statement", "win.opener", "a ie 6.0 patch", etc (THESE ARE ONES I RECEIVED TODAY ALONE - and it's only 7am!)
The only way to avoid this is not to post your email address publicly, or use a junk address when you do.
Some will harvest names and SELL them to these folks. Often freebie sites, contest sites, etc will do this.
Our isp lets us have an unlimited amount of addresses pointing to the domain(to our master email box), and we use a different one every time we give out the address; so we'll know who is selling it/giving it out. The address I gave for this site was TG@.....(mydomain). For PPFA I used ppfa@..... etc.. For Framer Select I use framers@... If one of these gets abused, I simply go to the isp administration program and I can block any of those aliases; so future emails go to ye ole bit bucket.
It's a very bad habit to open file attachments, unless you are specifically expecting something from someone you know. Even if its from someone you know, it could be an infected file. Most of the new infections cause your email program to send out the lil bugger to anyone in your contact list/phone book, disguised as something legitimate.
A virus scanner (such as Norton Antivirus) is no longer a luxury; but a necessity.
Just some ideas/opinion and hopefully an explanation of how they got your name...
WHY do they do it? GOOD QUESTION!
Mike