Spam continues to account for nearly 90 percent of the total email volume received by large enterprises, and attachment-based spam made a comeback, according to November data collected by Proofpoint, Inc., writes MarketingCharts (via MediaPost).

The Proofpoint Spam Index was at 88.17 percent in November, indicating that again nearly 9 of 10 email messages delivered to large enterprises were spam, though down from October's index of 89.04 percent.

Spam based on attachments — e.g., image, PDF and Microsoft Word files — increased in November over October levels, Proofpoint found:

• Image-based spam continued to rise for the second consecutive month, increasing to 10.0 percent of total spam volume, up 23.8 percent over October.
• Microsoft Word document spam (.doc attachments) rose by 64.6 percent over October levels and accounted for 4.7 percent of total spam volume.
• Microsoft Word document spam in .rtf format also increased, accounting for 0.62 percent of total spam volume (a 265 percent increase over October levels).
• PDF spam, while still a very small percentage of total spam volume, rose to its highest levels since September: Up 101 percent over October levels and accounting for nearly 1.8 percent of total spam volume.
• MP3 spam (the spammer's message is attached as an MP3 audio file) declined since its debut in October, accounting for just 0.04 percent of total spam volume - down by 33.33 percent.