According to Eric Park, an abuse desk analyst with Symantec's US west coast operation, when security researcher Brian Krebs broke the storage about Rostock being downed last week, his firm observed a decline in overall spam traffic.
"On March 16, Symantec saw global spam drop 24.7% compared to March 15. On March 17, global spam volume dropped another 11.9% compared to March 16. Compared to a week prior, the volume on March 17 was down 40.4%", he said in his security blog.
Park went on to say that, there was a small rise over the weekend, owing to a weekend anomaly when the spam percentage is typically higher than on weekdays.
"Symantec has kept a close eye on spam volume since Rustock temporarily ceased activity back in December. When Rustock, along with two other botnets, `fell asleep' on December 26, we saw a big decline in spam volume", he added.
Infosecurity notes that Park was interviewed by the Malware City newswire back in January, when Symantec reported that Rustock spam had fallen below 0.5% of all spam.
And Park said at the time, other botnets also went quiet over the Christmas/New Year break, with the Lethic botnet having been quiet since December 28, and the Xarvester botnet going silent on December 31.