E-mail spam distributors continue to try to elude detection and deliver their unsolicited messages into people's inboxes but have made no real gains, security software maker Symantec Corp. says.

The overall level of junk e-mail in May remained consistent with previous months at an average of 65 per cent but image spam continued to decline, Symantec said in its monthly spam report, released Thursday.

Image spam — whose message is sent as an image to slip past text-based filters — fell to an average of 16 per cent of e-mails sent in May, continuing the downward trend from previous months.

In April, 27 per cent of the spam Symantec detected was composed of images, down from 37 per cent in March. The security firm in January estimated as much as 52 per cent of spam was sent as images.

As the image spam declines, Symantec said it has observed a rise in the amount of spam that embeds internet links to images that contain the message the junk e-mailers are trying to deliver.

"Unfortunately, we do not have a specific percentage on the trend of linking to external images," Doug Bowers, senior director of anti-abuse engineering at Symantec, said in a statement e-mailed to CBC News Online. "Our analysts have observed an increase, but we are not currently tracking it as a separate category from a metrics perspective."

Meanwhile, the security researchers found that scam and fraud e-mail rose to 13 per cent in May, up from nine per cent in March.

The report also notes that scam e-mails in the "Asia-Pacific and Japan" region are 17 per cent of spam there — nearly double the global figure of nine per cent.

Symantec defines scam e-mails as those that are known to trigger fraudulent activity by the sender, such as Nigerian investment, pyramid scheme or chain letter spam. Fraud spam is also known as phishing e-mail, which is typically crafted to appear as though it comes from a well-known company in a bid to gain the potential victim's confidence.

So-called 419 spam — named after an article of the Nigerian Criminal Code that deals with fraud in light of a tidal wave of e-mails that has claimed unwitting victims in recent years — has gained another version.

In its latest incarnation, 419 spam attempts to coax funds from would-be dupes with the promise of employment as a funds transfer agent.