The tactic, used in the Afghan badlands of Helmand, was exposed by Tory MP and ex-Army officer Patrick Mercer.
Speaking of stooping to depths, this would be the same Patrick Mercer that continued to work with the discredited Glen Jenvey for 2 months after he had sold the "TERROR TARGET SUGAR" story to the paper, a report which he had entirely concocted himself after posting on the Ummah.com web forum. Mercer gave credibility to Jenvey's "investigations" by helping him make contact with various tabloid newspapers, many of which it should be doubted were anything approaching accurate. When Mercer has been involved in such dubious actions in the past, that on its own should put newspapers on alert as to how reliable such completely unverifiable claims are. That it also involves much the same tall tales that Jenvey pushed ought to be another red line, but after all, it is the Sun we're talking about here.
Regardless of its veracity, the story has now been churned all over the globe and is the paper's second most read page, a position usually held by either sport or something involving sex. Perhaps those paywalls aren't the best idea after all? Shame you have to print such fabulous nonsense to get any such attention.
Update: Those more diligent, less dismissive and with more time than myself looked rather further into this, including this parish's own Richard Bartholomew, Tabloid Watch, but most crucially Jeff Schogol, who asked Patrick Mercer, the ISAF in Afghanistan and the Joint IED Defeat Organization for more details.
As could have been expected, Mercer's words, however the Sun got hold of the story, had been rather sexed up. Talking to Stars and Stripes he said it wasn't even a weapon as such, with the needles and razor blades most likely put in position around "dummy" devices. This was naturally translated by Tom Newton Dunn into "if the bomb goes off, the needles become deadly flying shrapnel". Mercer learned about these "HIV bombs" from bomb disposal technicians training to go to Afghanistan, not from those actually in the field, and while he didn't ask whether the Taliban had actually used such devices, he "got the impression" they were.
Predictably, the ISAF themselves had heard absolutely nothing about any such bombs, not even the dummy devices Mercer had thought were being used. "No reports, no intel, nothing" is a fairly good summary. Likewise, the Joint IED Defeat Organisation had no confirmed reports, but said it wasn't unusual for the Taliban to use "anti-tamper" devices, which are most likely not even closely related to used hypodermic needles.
Worth noting is that the quote from Deborah Jack at the end of the Sun's piece, making clear that catching HIV from a disposed needle is about as likely as the Sun not embellishing a story, was added after I first made this post, presumably for the print edition and most likely by a sub-editor who felt it needed a little balance. As the Rumor Doctor has it, "more like an enemy propaganda campaign than a widespread new tactic", and if there's one thing the Sun has always been good at, it's running propaganda campaigns.