The volume of spam has dropped steadily since August, but the Christmas period saw a precipitous decline.
One security firm detected around 200 billion spam messages being sent each day in August, but just 50 billion in December, BBC reported. While the reasons for the decline are not fully understood, spam watchers warn the lull may not last.
Around the Christmas holidays, three of the largest spam producers curtailed their activity, Paul Wood, a senior analyst at Symantec Hosted Solutions said. "But it's hard to say why," he added.
The vast majority of spam is sent by networks of infected computers known as botnets. One of these botnets, known as Rustock, was at its peak responsible for between 47 per cent to 48 per cent of all spam sent globally, Wood said.
In December, Rustock was responsible for just 0.5 per cent of global spam, he said. At the same time, two other prominent spamming botnets, Lethic and Xarvester, also went quiet.
There have been huge drops in spam levels before, said Wood. "Usually they have been associated with the botnets being disrupted. As far as we can tell Rustock is still intact," he added.
That means those controlling Rustock could have continued churning out masses of spam, but for whatever reason, have chosen not to, the report said. One possible explanation is that the spammers are simply regrouping ahead of a new campaign. Spammers are driven entirely by profit, said Carl Leonard, a researcher at security firm Websense.
"So if a campaign is not getting the returns they want, they can stop, regroup and try something else." he said. "For years there have been predictions that e-mail spam is set to decline," said Leonard.
"But for as long the spammers can generate profit from their activities, it's not going away." Wood said new spammers usually pop up to replace inactive ones. "We've yet to see any evidence that spam has become a bad business to be in," he added.