Bulk e-mail using attachments in the Portable Document Format (PDF) has
begun to decline just a month after it first appeared, and spammers are
moving on to Excel files, security firms said this week.

The seemingly short-lived adoption by spammers of PDF attachments began in mid-June, and peaked earlier this month.
However, use of the format has started to decline, while an increasing
amount of spam e-mail has appeared with Excel attachments. Enterprise
security firm BitDefender noted the decrease in PDF spam on July 24 and predicted that the format will cease being a significant vector in the future.