A Russian man suspected of helping run and create the Kelihos botnet has proclaimed his innocence.
Last week, Microsoft issued an amended complaint at the US District Court for the Eastern District of Virginia claiming former antivirus professional Andrey N Sabelnikov was "responsible for the operations of the Kelihos botnet."
Sabelnikov has subsequently posted a blog on LiveJournal, saying he was "dismayed" at being named a suspect.
We look forward to seeing Mr Sabelnikov in court so we can continue this discussion.
The Russian claimed he "did not commit this crime" and had "never participated in the management of botnets."
Sabelnikov said he had been over to America on business in late January when Microsoft lodged the complaint, but decided to return to Russia as he could not afford legal assitance in the US.
He added he was ready to answer questions relating to Kelihos.
The Kelihos botnet was shut down last year, but Microsoft has continued to hunt for the perpetrators and have them prosecuted.
Microsoft had previously accused Dominique Piatti, a Czech man running the dotFREE domain hosting company, claiming his business was registering subdomains used to operate Kelihos.
However, Microsoft came to the conclusion dotFREE was simply being used by Kelihos's controllers and came to an agreement with Piatti.
Cooperation with Piatti led to this week's fresh allegations against Sabelnikov.
At its peak, the Kelihos spam engine had infected an estimated 40,000 machines.
In response to Sabelnikov's claims, Microsoft said it stood by its original complaint and it looked forward to seeing the Russian in court.
"As this is a case pending in court, we cannot comment further except to say that we look forward to seeing Mr Sabelnikov in court so we can continue this discussion," Richard Boscovich, senior attorney for Microsoft's Digital Crime Unit, told the BBC.
Read on for our look at the war on botnets.
Get the ITPro. daily newsletter
Receive our latest news, industry updates, featured resources and more. Sign up today to receive our FREE report on AI cyber crime & security - newly updated for 2023.
Tom Brewster is currently an associate editor at Forbes and an award-winning journalist who covers cyber security, surveillance, and privacy. Starting his career at ITPro as a staff writer and working up to a senior staff writer role, Tom has been covering the tech industry for more than ten years and is considered one of the leading journalists in his specialism.
He is a proud alum of the University of Sheffield where he secured an undergraduate degree in English Literature before undertaking a certification from General Assembly in web development.