"Vendors should look through brouhaha calling for them to defend against each type of image spam and build products that attempt to capture the fundamental properties of spam," said Wang. "They can use techniques such as intent analysis and URL reputation analysis; those factors won't change with each new type of campaign that's being invented."
While conceding that the fight against spammers isn't one that will ever likely draw to a close, companies such as ISPs that are working harder than ever to keep unwanted e-mail from reaching their customers say that progress is being made.
Stephen Currie, director of product management for e-mail, at Atlanta-based ISP EarthLink, which reported 2006 revenues of more than $1.3 billion, said that his company has been able to reduce the amount of spam reaching its customers by 80 percent in the last 18 months.
Using filtering tools sourced from San Francisco-based software maker Cloudmark and its internally developed Scamblocker.com anti-phishing resource, along with a heavy dose of input from its users, has allowed the firm to turn up the heat on image spam and other AI campaigns, he said.
"The message content fingerprinting technologies from Cloudmark allow us to understand message contents without ever opening them up, and it doesn't require as much CPU power on our end as it would have even several years ago," Currie said. "But the real key has been to become very aggressive about using the feedback we get from end-users to stop spam that initially finds a way through."
Just as CAPTCHA relies on human interaction to defeat automated input, the approach of using customer feedback to identify and block spam sources is one that has trumped technological means, the executive said.
"Once we determine the root source of a campaign using these types of methods, we can block a lot of the IP addresses being used to stop it from sending additional mail to our servers," Currie said. "Although we're getting shipped more spam than ever, customers are telling us that they're now getting less than over the last several years, but we absolutely expect new things to come along and challenge us; it's the proverbial cat-and-mouse game."
In addition to utilizing human and technological means to stop spam, EarthLink is also involved in the Messaging Anti-Abuse Working Group (MAAWG), a global ISP initiative aimed at improving the current state of electronic messaging.
In mid-May, the group released its latest Sender Best Communications Practices (BCP), a set of best practices for e-mail technologies and subscription methods meant to improve deliverability rates for legitimate newsletter and marketing messages.
Officials with San Carlos, Calif.-based e-mail security service provider Postini -- which claims to process more than 1 billion messages per day for more than 35,000 organizations -- said that spam levels continue to set new records and that unwanted e-mails currently account for roughly 90 percent of all traffic it monitors, with 40 percent of those messages containing image spam.
In addition to high levels of image spam, the company is also tracking developments such as an increase in the volume of messages that appear to be meant to harvest e-mail addresses for subsequent malware attacks, including botnet threats.
Other recent trends under investigation by the firm include spam that attempts to evade filtering tools by using strings of gibberish to confuse content scanning technologies.
The company maintains that its products can help customers catch up to 99 percent of all spam if they are willing to employ the most aggressive settings available, but Postini executives said that users' fear of missing legitimate messages forces most companies to seek a balance between warding off unwanted e-mail and toning down the possibility for false positives.
"Because the overall volume of spam continues to increase, clients are seeing a few more messages per day sneaking in, and it does tend to be image spam, but progress is being made," said Adam Swidler, Postini's senior manager of solutions marketing. "It's probably naive to think that this fight will ever end as long as there is a monetary driver for the bad guys, but we do think that we can help get to a place where spam is only a minor nuisance."