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.
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 Services told BBC News.
"But it's hard to say why," he added."