Horizon Blue Cross Blue Shield of New Jersey, an insurer, has invited members to participate in the project at Hackensack University Medical Centre. The company hopes that it will "save lives and provide a measure of comfort to our members with chronic conditions and to their families".

Laudable stuff - but in its wake trail issues of privacy, power and autonomy. Will future patients have to be chipped as a condition of insurance cover? Also, these chips, which can be read through clothing, are RFIDs - radiofrequency identification devices. The signals they emit can be picked up 30ft away without the "chippee" knowing; a delight for stalkers.

VeriChip, the company providing the chips, has already seen its products used by anxious parents wishing to track their kids, by employers who want their workers to have keyless access to secure areas and by Hurricane Katrina rescue workers, who chipped unidentified bodies.

Now consider that Scott Silverman, president of Verichip, recently suggested that the US Government use the RFIDs to track migrant workers coming from Mexico. Interestingly, Tommy Thompson, the former US Secretary for Health and Human Services, skipped over to VeriChip's board after leaving office, and then suggested that every American should be chipped. With ID cards in Britain on the verge of being scrapped, and Home Office hysteria over unwanted visitors, could identity chips take over as the fresh scourge of the civil libertarians?

The newest spam uses technology that varies the content of individual messages - through colors, backgrounds, picture sizes or font types - so they appear to be distinct to spam filters. The spam is delivered to consumers and companies through millions of compromised PCs, called bots.

As a result, the messages are like snowflakes: No two are alike, says Julian Haight, founder of anti-spam organization SpamCop.

The surge in new spam has largely eluded software filters and eaten up space on e-mail systems because each message is more than seven times larger than regular spam, Sprosts says.

Most image-based spam comes in the form of stock scams, which contain the same basic language within a shaded box.

Much of it comes from spam gangs in the USA and Russia, Sprosts says.

Stock scams make up about 20% of spam - about twice the share at the start of the year, IronPort says.

Until last year, image spam was rare. Though it had been around for about four years, spammers lacked the technology to randomize images, says Dmitri Alperovitch of e-mail security company CipherTrust. Before, spammers included a link on e-mail spam to direct recipients to a site containing pictures.

Not anymore. The new spamming tactic is the latest salvo in the battle between junk e-mailers and filter developers. As software gets better at identifying and blocking spam, spammers get smarter at outfoxing software.

"It is a never-ending cat-and-mouse game," Alperovitch says.