The Dridex botnet, which targets financial credentials, appears to be gaining steam again, striking computers in the U.S., U.K. and France.
Trend Micro is the latest security vendor to say it is seeing Dridex activity after the U.S. Department of Justice said last month it had significantly disrupted it in a joint action with the U.K.
Sometimes referred to as Cridex or Bugat, Dridex is advanced malware that collects financial login details and other personal information that can be used to drain bank accounts.
Trend has seen multiple spam campaigns sending out malicious attachments, such as Excel or Word documents, that could install Dridex, wrote Ryan Flores, a threat research manager.
The spam emails use social engineering to try to get people to open purported invoices, unpaid bills, receipts or financial statements, he wrote.
Dridex can be hired out by other cybercriminals who want to compromise computers. Those campaigns are identified by codes.
Flores wrote that Trend Micro noticed codes used in recent spam runs that were also seen as far back as Oct. 14.
"This development further validates previous findings that the Dridex botnet was not totally taken down," he wrote.
The top countries targeted by Dridex spam are the U.S, U.K., France and Australia, Trend said.
Palo Alto Networks noticed that Dridex activity fell in September, preceding the DOJ's announcement, but picked up again by early October.
Botnets can be difficult to eradicate. Even if network resources used by the cybercriminals are taken offline, they often set up new infrastructures to begin compromising computers again.
The DOJ accused Andrey Ghinkul, 30, of being the administrator of the Dridex. Ghinkul was arrested on Aug. 28 in Cyprus, and the U.S. is seeking his extradition to face a nine-count indictment in the U.S. District Court for the Western District of Pennsylvania.