Separate research by security vendors McAfee and Marshal Software suggests that the industry is winning the war on spam, with two of the most common forms of spam-related scams on the decline.
Instances of "pump 'n' dump" financial fraud spam has plummeted from 50 percent of all spam in February to just five percent today.
"Pump 'n' dump" is the name given to spam e-mails distributed by online fraudsters looking to boost the share price of thinly-spread, small cap stocks.
The scam, often linked to mafia criminal groups, has essentially been around since even before the Internet (via cold-calling rather than e-mail). It reached its online peak in February of this year -- representing half the total spam in circulation.
But an analysis of some six million e-mails per week conducted by Marshal Software's TRACE team shows that the scam now only represents 5.1 percent.
Bradley Antsis, director of product management at Marshal, said the joint efforts of financial regulators and anti-spam vendors are responsible for the decline.
In March of this year, the US Securities and Exchange Commission (SEC) announced a campaign dubbed "Operation Spamalot" -- suspending the trading in 35 companies targeted by pump 'n' dump spam this year.
The SEC estimated at the time that around 100 million pump 'n' dump spam messages are sent every week, "triggering dramatic spikes in share price and trading volume before the spamming stops and investors lose their money".
"Now that fewer stock spam messages are making it through spam filters and more end users are savvy to the spam technique and less inclined to be sucked into the scam, spammer's gains have likely dwindled," said Antsis.
"Subsequently the risks associated with the investment needed for stock spam make it no longer as attractive to spammers."
Image-based spam, in which unsolicited e-mails evade anti-spam filters by including their messages within attached images, is also on the decline according to McAfee.
At the start of the year, McAfee suggests that image-based spam was responsible for 65 percent of unsolicited e-mail (around 50 percent, according to Marshal).
McAfee said that image-based spam is now on the decline -- and Marshal estimates it now represents less than 20 percent of total spam.
Unfortunately, Marshal claims that despite two of the most prevalent forms of spam declining drastically, the total volume of spam remains the same, if not slightly higher.
Much of the remaining image-based spam is being delivered as a link rather than attachment, and many spammers have retreated to traditional text-based messages, the company said.