Like the typical office worker, the output of email attackers drops well below the average on Saturday and Sunday, picks up pace on Monday and then peaks on Wednesday.

"It seems these attackers don't like to work on weekends, either. Monday's attack level is average, while the midweek spike tapers off to below average levels by Friday," FireEye senior staff scientist, Darien Kindlund, wrote in a recent , which looked at the first quarter of 2012.

The spike across Wednesday and Thursday was up to four times higher than the average volume between January to May. While volumes varied, FireEye's analysis shows a consistent trend of activity peaking in the middle of the week.

The company had previously noted a correlation between an increase in malicious emails in line with US public holidays. Building on its theory that there is a link between holidays and a rise in attacks, Kindlund noted that the most active week for "advanced persistent" or targeted attacks came in mid-March, a week ahead of North America's spring break.

The good news, according to FireEye's figures, is that malicious email volumes are well down on the same period in 2011, when fake antivirus campaigns were the dominant class of email carried threats.