Fresh off releasing new stats showing that more than half of machines once infected with the Rustock trojan have been cleaned, Microsoft is turning its attention to finding the masterminds responsible for the botnet.
The software giant is offering a $250,000 (A$235,000) reward for information that leads to the arrest and conviction of the Rustock operators, Microsoft senior attorney Richard Boscovich announced Monday in a blog post.
The move follows a Microsoft-led takedown operation in March, which involved cutting off command-and-control centers from being able to communicate with Rustock-infected machines and filing a lawsuit against 11 unnamed defendants.
"Microsoft has already been gathering strong evidence in our ongoing investigation, and this reward aims to take that effort a step further," Boscovich wrote. "We will continue to follow this case wherever it leads us and remain committed to working with our partners around the world to help people regain control of their Rustock-infected computers."
According to the "Battling the Rustock Threat" report recently released by Microsoft, as of June 18, more than 700,000 IP addresses are infected with Rustock, down from more than 1.6 million on March 26.
At one point, Rustock was responsible for almost half of the world's spam, according to security firm Symantec.
In February 2009, Microsoft announced a reward of the same price for information that led to the capture of the creators of the then-fast-spreading Conficker worm.
The authors have not been caught.