You're not imagining things—there is more spam in your inbox these days.

A report released Monday by the computer security firm McAfee found that global spam volume is on the rise—and in the United States, it's being driven by surprising financial market catalyst.

According to the McAfee Threats Report for the first quarter of 2013, spam email volume rose "dramatically" in that time frame after three years of stagnation. One significant element driving the growth in North America, the firm said, was "the return of 'pump and dump' spam campaigns."

Those campaigns are designed to quickly focus investor attention on an obscure, thinly traded stock to create a sharp run-up in value. Typically, those scammers will buy the stock before sending the spam and then sell after the price pops, pocketing a quick profit.

And part of what's driving this surge in spam is scammers targeting people who are frustrated that they've missed out on the gains from the recent surging bull market. McAfee said it has spotted an increasing number of spam emails targeting would-be investors "hoping to capitalize on all time equity market highs." Also contributing to the surge: growth hormone offerings and increasing spam campaigns in emerging markets.