Updated The electronic tags used to keep tabs on criminals and suspects in the UK are "unreliable" - and the systems monitoring them are "shambolic". That's according to a dynamite report by Ross Anderson, a leading computer scientist.
The University of Cambridge professor said he compiled his findings after he was called in as an expert witness to defend a woman accused of tampering with a tag.
We're told the court case against her was dropped after Prof Anderson's devastating dossier [redacted PDF] highlighted the number of "false alarms" triggered by the tags' anti-tampering sensors - and the equipment's "unreliable back-end systems".
His testimony concluded that there was reasonable doubt that the woman tried to prise off the tag: a technical fault may have been to blame, or that the tag "having become overly sensitive, perhaps through wear and tear, did not require the 35kg of force to register a tamper, but merely some innocuous activity".
Each of the electronic gadgets is usually securely strapped to the ankle or wrist of a perp or someone released on bail, and it talks wirelessly to a monitoring unit typically installed in the wearer's home. If the tag isn't within range of this unit during the hours of evening curfew, the equipment alerts the firm contracted to provide the system.
Rather than put suspects behind bars, or keep crims in prison for their full sentences, people can be ordered to stick to a strict curfew and fitted with tags to keep them at home after dark. The technology first became available to courts in England and Wales in 1999.
'The overall impression is of an unreliable technology'
Serco, one of the main private security firms running the scheme, was monitoring more than 9,000 people a day in August 2012, and was the contractor who brought the aforementioned woman to court for allegedly "tampering with the tag", we're told.
About 18,000 people are electronically tagged at any one time, according to the security engineering prof. Typically, those subject to curfew orders need to stay at home from 8pm to 8am.
He said he was asked to write up an expert report on the evidence presented by Serco for last month's court case in London. According to his review, the tagging system relied too much on contractors and their partners, rather than independent parties, to investigate alleged breaches of the rules.
"[Serco's] logs relating to my defendant’s case showed large numbers of false alarms; some of these had good explanations (such as power cuts) but many didn’t," Prof Anderson explained in a blog post.
"The overall impression is of an unreliable technology surrounded by chaotic procedures.
"Of policy concern, too, is that the tagging contractor not only supplies the tags and the back-end systems, but the call centre and the interface to the court system. What’s more, if you break your curfew, it isn’t the Crown Prosecution Service that takes you before the magistrates, but the contractor – relying on expert evidence from one of its subcontractors. Such closed systems are notoriously vulnerable to groupthink."
The academic asked for access not just to the tag at the heart of this particular case, but to Serco's equipment for testing the electronics, plus system specifications, false-alarm statistics and audit reports. Serco demurred and decided to drop its prosecution, the prof said.
"If you’re designing systems on whose output someone may have to rely in court, you’d better think hard about how they’ll stand up to hostile review," he concluded in a post on his university's Light Blue Touchpaper blog here. The academic's previous work includes an investigation into phantom money withdrawals, which led to the discovery of weaknesses in systems banks had insisted were foolproof. ®
Since the publication of this article, Serco has contacted The Reg to defend the reliability of its technology. James Rutherford of Serco said: "The equipment we use for Electronic Monitoring is proven to be robust and reliable. Where there is evidence of tampering we will pursue offenders through the courts."