As any computer-user is aware, Spam is not just meat in a can, but the name given to all those emails cluttering your in-box, with enticements to grow body parts or get rich quick in the stock market.

Most are merely annoying but some carry dangerous malware and computer viruses. Where do they come from?

If you answered "Nigeria," because of that country's well-known 419 email scams, you would be wildly off the mark, according to the security experts at Sophos Software, who have compiled a "dirty dozen" list of countries that contribute more than their fare share of Spam email to the world. Nigeria isn't even on the list.

"What many people haven't learnt is that the spammers don't use their own computers to send spam - instead they create botnets of compromised PCs around the world (also known as "zombies"), which they can remotely command to spew out unwanted marketing messages, malicious links and even launch distributed denial-of-service attacks," Graham Cluley, a Sophos Security experts, writes in his blog.

That means Spam originates where there are the most infected computers, and according to Sophos, that's the United States. Here is the complete ranking:

1. USA (18.83%)

2. India (6.88%)

3. Brazil (5.04%)

4. Russia (4.64%)

5. UK (4.54%)

6. France (3.34%)

7. Italy (3.17%)

8. S. Korea (3.01%)

9. Germany (2.99%)

10. Vietnam (2.79%)

11. Romania (2.25%)

12. Spain (2.24%)

Rest of the world (40.17%)

"In all, we counted Spam being sent from an astonishing 232 countries around the world during the last quarter of 2010," Cluley writes. "So everyone, no matter where they are on the planet, should be taking more care of their personal computer's protection."

Cluley also reports what appears to have been a drop in Spam levels since Christmas. He said some botnets that had been pumping out Spam have suddenly stopped. That's not necessarily good news, he says, since they may be using the botnets for other, more sinister, activities.