We’ve been telling you a lot about spam recently, whether it’s image spam or PDF spam or Excel spam. It’s important to note that these tactics have only a few end-goals – usually downloading harmful software to a PC or sending pump-and-dump stock tips.

The researchers at Sophos filled us in on a spam outbreak they saw earlier this week that increased the amount of spam in its global traps by 30 percent in 24 hours.

The spam attack included an attached PDF file that urged recipients to buy penny shares in a company called Prime Time Group Inc. Of course, the spammers have already bought loads of the stock and are trying to inflate the price.

Here is a quote from Sophos’ Ron O’Brien, a senior security analyst, on the spike:

“While the prevalence of PDF spam campaigns has been slowing increasing, the volume of spam distributed with this particular attack is unusual. Typically the trend has been for smaller campaigns that continually evolve and modify themselves so that once one form has been detected others can still bypass spam filters - the recent e-card attack is a great example of this. As long as even a small percentage of people continue responding to pump-and-dump scams like this, the problem will continue to exist.”