Trojanized ESET Installers Drop Kalambur Backdoor in Phishing Attacks on Ukraine

A previously unknown threat activity cluster has been observed impersonating Slovak cybersecurity company ESET as part of phishing attacks targeting Ukrainian entities.

The campaign, detected in May 2025, is tracked by the security outfit under the moniker InedibleOchotense , describing it as Russia-aligned.

"InedibleOchotense sent spear-phishing emails and Signal text messages, containing a link to a trojanized ESET installer, to multiple Ukrainian entities," ESET said in its APT Activity Report Q2 2025–Q3 2025 shared with The Hacker News.

InedibleOchotense is assessed to share tactical overlaps with a campaign documented by EclecticIQ that involved the deployment of a backdoor called BACKORDER and by CERT-UA as UAC-0212 , which it describes as a sub-cluster within the Sandworm