According to the Official Google Enterprise Blog:

“Last quarter we reported on the trend toward larger message sizes, measured in bytes. The trend has continued into this quarter, making 2009 a year of resurgence in old techniques such as image spam and payload viruses. When considering the spam bytes processed per user, growth has been steep in 2009, with Q3’09 rates up 123% from Q3’08.”

For anyone who’s wondered why spammers consider to spam, consider this from the Google report:

“The majority (55%) of these viruses are messages like the one you see below, a fake notice of underreported income from the IRS (which the IRS distributed an alert on earlier this week). Another large contingent (33%) have come in the form of fake package tracking attachments, which were already on the rise in Q2. You might think a spoofed IRS notice or package tracking email is obviously spam, and wonder who would fall for it and actually click on the attachment.

However, at these volumes, it takes only a tiny fraction of the recipients being fooled for the spammers to add hundreds of computers to their botnets every day.”

Click here to read the full report at the Official Google Enterprise Blog.