The trouble was 36 Cobalt-60 sources with a combined radioactivity of 3,500 curies. A single source is powerful enough to kill a person within minutes of direct exposure.
The irradiator once sterilized male Mediterranean fruit flies. When the project ended all knowledgeable staff left the institute, abandoning the Cobalt-60 in shielded containers safe from contamination—only the containers themselves were not secured in the building.
IAEA officials originally identified problems in 2006. But after the first first-fact finding mission Israel bombed the airport and the recovery project had been on hold ever since waiting for Lebanon to normalize. On 30 August the Cobalt-60 was finally flown to a secure storage facility in Russia.
Hope that's not an oxymoron.
At any rate, the Lebanese operation is part of a wider initiative to secure radioactive materials from scientific research, medicine, and industry that might be used to make dirty bombs.