US sees junk mail lead shrink.

The number of spam messages originating from computers in China has surged over the past month, and security experts are warning that the country may emerge as a spamming superpower.

The rise in spam volumes ends what had been an encouraging period for China. Security firm McAfee reported in December that state enforcement agencies had cracked down on spammers, causing many messages to appear with the malware links already taken down.

In January, however, McAfee said that a new rash of pharmaceutical spam erupted from China. The company is not yet sure as to the origin of the messages.

"Although Chinese computers are not being used for spam they way they were last year, we are seeing a resurgence which is now putting them in the lead, ahead of the US," said McAfee Avert Labs senior vice president Jeff Green.

"Also, although these zombie computers are not being used for spam, you have to wonder whether they are being used for another purpose."

Systems in China were linked to a spam run targeting US president Barack Obama last month. The messages purported to link to a story about Obama's refusing to become president, in an attempt to lure users to a malware site.

China was not the only country making waves in the spam world last month. Researchers also noted a flood of emails offering 'cheap software' that was eventually traced back to systems in Switzerland.

Meanwhile in the US, Microsoft's Windows Live service was abused by spammers to host pages for pharmaceutical spam.