Security firm Symantec has warned that botnets like Bagle are stepping in to fill the void created the recent dismantling of Rustock.

As per some estimates, worldwide spam levels dropped 33 per cent when Rustock, which used to send as many as 13.82 billion spams daily, was taken down in a Microsoft-led operation in mid-March.

Different estimates suggest that 83 per cent of worldwide spam came from botnets so far this year. The figure is up from 77 per cent at the end of last year.

According to a fresh report by Symantec, “Botnets have been and remain a destructive resource for cyber criminals and through the years have become the spammers’ air-supply, without which it would be very difficult for them to operate.”

Rustock is now out of the way, but the list of ruinous botnets is still very lengthy, with Bagle, Festi, Cutwail and Lethic at the top of the list. These four botnets jointly account for more than 16 billion spam messages daily.

What is more dangerous is the big number of e-mails with viruses and malicious links that infects that host computers and gives their control in the hands of hackers.

As per Symantec’s claims, the worldwide ratio of e-mail borne viruses in e-mail traffic was 1 in 208.9 e-mails in March.