India has overtaken the US to become the world's top source of junk or unsolicited emails, accounting for one in ten spam messages in the inbox, research by a security firm has found.

Research conducted by Sophos, covering the first quarter of 2012, found that the number of messages that spread malware or represent more targeted attempts to phish usernames, passwords and personal information is increasing. However, basic marketing spamming is showing a declining trend.

The downward trend is attributed to the changing tactics of spammers who are increasingly finding traditional email spam ineffective and turning to social networks to spread marketing spam campaigns.

Most spam comes from home computers that have been compromised by hackers. India's rise to the top spot was fueled by the rising number of new Internet users in the country. The results also suggest that computers in the country are not properly protected and that ISPs are not taking spam as seriously as they should, Sophos said in a statement Monday.

While traditional marketing spam may appear to be no more than an annoyance, offering pills that have questionable claims or 'get rich quick' schemes, they can often lead to more serious threats to your personal information, said Graham Cluley, senior technology consultant at Sophos. The latest stats show that, as more first-time Internet users get online in growing economies, they are not taking measures to block the malware infections that turn their PCs into spam-spewing zombies.

Zombies are the infected computers that form networks called botnets. Botnets are used by cybercriminals to send spam, steal information and launch DDoS denial of service attacks.

The top 12 spam-relaying countries for January to March 2012:

1. India - 9.3%

2. US - 8.3%

3. South Korea - 5.7%

4. Indonesia tied with Russia - 5.0%

5. Italy - 4.9%

6. Brazil - 4.3%

7. Poland - 3.9%

8. Pakistan - 3.3%

9. Vietnam - 3.2%

10. Taiwan - 2.9%

11. Peru - 2.5%

12. Other - 41.7%

Top spam-relaying continents for January to March 2012:

1. Asia 46.7%

2. Europe 26.9%

3. South America 11.9%

4. North America 10.9%

5. Africa 3.0%

6. Other 0.6%