According to Spamhaus, these are the worst spammers out there

1. Canadian Pharmacy – Ukraine
2. yair Shalev / Kobeni Solutions – United States
3. Century Infotech – India
4. Jagger Babuin / BHSI – Canada
5. Dante Jimenez / Aiming Invest – United States
6. Yambo Financials – Ukraine
7. Vincent Chan gang – Hong Kong
8. First Place SEO & financial fraud spam gang – United States
9. Michael Lindsay / iMedia Networks – United States
10. Josh Henderson or Nicholson – bulletproofvps.com – Canada

Source: The Spamhaus Project