Kelly Conley of Symantec Security Response blogged on Friday that her company has seen the percentage of PDF-attachment spam jump from zero percent at the beginning of October to two percent in the past week.

The small spike might be the result of one PDF pump-and-dump stock scam that sent out over 20,000 messages.

Here’s a breakdown of what Symantec has seen in relation to this trend, according to Conley:

“PDF spam was widely observed in June, reached a peak in early August and then began a decline through September where by the end it was barely a blip on the radar. Now in the earlier days of October, we are closely monitoring this small revival of PDF spam that is currently being observed.”