Security Experts:

Kelihos Botnet Triples in Size Overnight

The Kelihos botnet has kept a low profile following takedown attempts a few years ago when it was highly active, but has shown significant spikes in activity recently, MalwareTech warns.

The botnet’s infections remained very low over the past years, while the activity it focused on was spamming stock pump and dump schemes or pharmaceutical scams, researchers say. Following each campaign, the botnet would remain dormant for weeks or months, but this modus operandi has changed in mid-June, when Kelihos started spamming other malware.

The recently spotted Wildfire ransomware was distributed via Kelihos, which MalwareTech says was very unusual: “the ransomware itself appears to be the work of scriptkiddies (the code is very amateur, it utilizes the .Net framework, and the C&C servers are hosted using a shared hosting sold on an English language scriptkiddie forum); these are not the sort of people you’d expect to be involved with a Russia spam veteran.”

However, after the Wildfire campaign went down, the botnet started spreading other ransomware, along with banking Trojans based on the Zeus source code, the security firm says. The change might be the result of Kelihos’ operator finally realizing that ransomware and banking Trojans are more profitable than pump and dump spam.

The increase in Kelihos infections started when the botnet was still dropping the Wildfire ransomware, but remained very small between June 27 and July 5, MalwareTech says. Starting on July 11, however, an aggressive campaign kicked off, resulting in the botnet’s size growing from around 8,000 infections to around 13,000.

The size remained steady for more than a month, followed by a massive spike on August 22, when 16,000 new infections were registered in only 3 hours (9,000 of them in the first 10 minutes). Kelihos continued to grow over the 24 hours following the initial spike, and the botnet reached a total of 34,533 infections.

The campaign doesn’t appear to have been targeted to a specific geography.

“When mapped out the data reads like any other indiscriminate malware campaign with infections tied mainly to global population centers and the majority in developing countries,” MalwareTech explained.

Chances are that the Kelihos operator started spamming the Wildfire ransomware to test whether they should join the rest of the major spam botnets in the current campaigns focused on delivering ransomware and banking Trojans. Moving forth, the botnet’s infections are expected to increase, as the operator is attempting to deliver higher volumes of spam.

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