An al-Qaeda list of 22 tips on how to avoid drones, left behind by Islamic extremists as they fled northern Mali last month, has been found.
A copy of the document, which was first published on a jihadist forum two years ago, was found by The Associated Press in a manila envelope on the floor of a building occupied by al-Qaeda of the Islamic Maghreb.
The tipsheet reflects how al-Qaeda's faction in north Africa anticipated a military intervention that would make use of drones, as the battleground in the war on terror worldwide is shifting from boots on the ground to unmanned planes in the air.
The presence of the document in Mali, first authored by a Yemeni, also shows the coordination between al-Qaeda groups, which security experts have called a source of increasing concern.
"This new document ... shows we are no longer dealing with an isolated local problem, but with an enemy which is reaching across continents to share advice," said Bruce Riedel, a 30-year veteran of the CIA, now the director of the Intelligence Project at the Brookings Institution.
The tips in the document range from the broad (hide from being directly or indirectly spotted, especially at night) to the specific (formation of fake gatherings, for example by using dolls and statues placed outside false ditches to mislead the enemy).
The use of the mats appears to be a west African twist on number three, which advises camouflaging the tops of cars and the roofs of buildings, possibly by spreading reflective glass.
While some of the tips are outdated or far-fetched, taken together, they suggest the Islamists in Mali are responding to the threat of drones with sound, common-sense advice that may help them to melt into the desert in between attacks, leaving barely a trace.
"These are not dumb techniques. It shows that they are acting pretty astutely," said Col Cedric Leighton, a 26-year-veteran of the US Air Force, who helped set up the Predator drone programme, which later tracked Osama bin Laden.
"What it does is, it buys them a little bit more time - and in this conflict, time is key. And they will use it to move away from an area, from a bombing raid, and do it very quickly."
The success of some of the tips will depend on the circumstances and the model of drones used, Col Leighton said.
For example, from the air, where perceptions of depth become obfuscated, an imagery sensor would interpret a mat stretched over the top of a car as one lying on the ground, concealing the vehicle.
New models of drones, such as the Harfung used by the French or the MQ-9 "Reaper," sometimes have infrared sensors that can pick up the heat signature of a car whose engine has just been shut off.
However, even an infrared sensor would have trouble detecting a car left under a mat tent overnight, so that its temperature is the same as on the surrounding ground, Col Leighton said.
Unarmed drones are already being used by the French in Mali to collect intelligence on al-Qaeda groups, and US officials have said plans are under way to establish a new drone base in northwestern Africa.
The US recently signed a "status of forces agreement" with Niger, one of the nations bordering Mali, suggesting the drone base may be situated there and would be primarily used to gather intelligence to help the French.
The author of the tipsheet found in Timbuktu is Abdallah bin Muhammad, the nom de guerre for a senior commander of al-Qaida in the Arabian Peninsula, the Yemen-based branch of the terror network.
The document was first published in Arabic on an extremist website on 2 June, 2011, a month after bin Laden's death, according to Mathieu Guidere, a professor at the University of Toulouse.
Mr Guidere runs a database of statements by extremist groups, including al-Qaida in the Islamic Maghreb, and he reviewed and authenticated the document found by the AP.
The tipsheet is still little known, if at all, in English, though it has been republished at least three times in Arabic on other jihadist forums after drone strikes took out US-born cleric Anwar al-Awlaki in Yemen in September 2011 and al-Qaida second-in-command Abu Yahya al-Libi in Pakistan in June 2012.
It was most recently issued two weeks ago on another extremist website after plans for the possible US drone base in Niger began surfacing, Mr Guidere said.
"This document supports the fact that they knew there are secret US bases for drones, and were preparing themselves," he said.
"They were thinking about this issue for a long time."
The idea of hiding under trees to avoid drones, which is tip number ten, appears to be coming from the highest levels of the terror network.
In a letter written by Bin Laden and first published by the US Center for Combating Terrorism, the terror mastermind instructs his followers to deliver a message to Abdelmalek Droukdel, the head of al-Qaida in the Islamic Maghreb, whose fighters have been active in Mali for at least a decade.
"I want the brothers in the Islamic Maghreb to know that planting trees helps the mujahedeen and gives them cover," Bin Laden wrote.
"Trees will give the mujahedeen the freedom to move around especially if the enemy sends spying aircrafts to the area."