MessageLabs concludes that the decrease comes after the dismantling of Rustock, one of the most stubborn and technically sophisticated botnets on the malware landscape.

The firm said, however, that web-based malware is still on the increase in Hong Kong and mainland China.

Spamming is a challenging issue for netizens and last year Rustock was responsible for as much as 47.5 per cent of all spam. EBA claims that in 2010, Rustock sent about 44.1 billion spam emails each day.

But this decrease does not mean increase in web security as according to Harry Pun, Client Services manager, North Asia for Symantec.cloud, He says other botnets have stepped up their activities to take advantage of the gap in the market created by the Rustock takedown.

"Since the end of 2010, the Bagle botnet has been more active, sending approximately 8.31 billion spam emails each day, the majority of which linked to pharmaceutical products," said Pun. "While Bagle may not have as many bots under its control or have spikes of traffic as large and dominating as Rustock, its output has been more consistent. In the wake of Rustock's demise, Bagle has already taken over from Rustock as the most active spam-sending botnet in 2011."