US investigators have demanded security firm F-Secure only reveal slim details on the Conficker worm at a Black Hat presentation.
The request comes as police continue their work investigating the origins of the worm, which infected millions of Windows machines since late last year.
A source close to F-Secure told Reuters that Mikko Hypponen, the company's chief research officer, was asked not to divulge details about the worm's origins and the Conficker gang's motives.
Earlier in the day, F-Secure's blog said Hypponen would be speaking about Conficker (also known as Downadup), a worm that the company has tracked closely.
The last-minute change of plans for Hypponen is nothing new at Black Hat, which has been the site of numerous speech-blockings and speech-blocking attempts, including that of a researcher Cisco sued because he was to reveal a flaw in the company's IOS code.
Conficker's culprits are also the target for a $250,000 bounty offered by Microsoft.