Connect with us

Hi, what are you looking for?

SecurityWeekSecurityWeek

Email Security

Necurs Botnet Fuels Massive Year-End Ransomware Attacks

The Necurs botnet started 2017 with a four-month vacation, but ended the year sending tens of millions of spam emails daily as part of massive ransomware distribution campaigns.

The Necurs botnet started 2017 with a four-month vacation, but ended the year sending tens of millions of spam emails daily as part of massive ransomware distribution campaigns.

Considered the largest spam botnet at the moment, Necurs was the main driver behind the ascension of the Locky ransomware (which in turn is associated with the Dridex banking Trojan) in 2016. As Necurs took a long vacation in the beginning of 2017, Locky was silent as well, but both resumed activity in April.

Over the course of 2017, however, the botnet was involved in the distribution of the Jaff, GlobeImposter, and Scarab ransomware families, as well as in ‘pump-and-dump’ schemes.

Over a 10-day period between December 19 and December 29, 2017, Necurs was once again involved in the distribution of ransomware, in addition to sending typical holiday-themed scam emails, data collected by AppRiver reveals.

The messages, AppRiver says, were distributing the Locky and GlobeImposter ransomware families and revealed the attackers’ preference to use malicious .vbs (Visual Basic Script) or .js (JavaScript) files located inside a .7z archive.

Consisting of between 5 and 6 million infected hosts and keeping around 1 or 2 million of them active at any given time, Necurs provides operators with remote access to the infected machines and can be used for various malicious activities, including malware downloads.

Starting on Dec. 19, the botnet was observed sending tens of millions of spam emails daily to distribute ransomware. It started at nearly 46 million emails on the first day (peaking at over 4.6 million messages per hour) and continued with over 47 million messages on Dec. 20 (peaking at 5.7 million per hour).

Advertisement. Scroll to continue reading.

While the initial spam featured mainly .vbs files inside the .7z archive, .js files started appearing as well on the second day, and the traffic switched to .js files on Dec. 21-22, when it also started to taper off, at 36 million and 29 million messages per day, respectively. The botnet remained quiet from Dec. 23-25 and recommenced activity for only a couple of hours on Dec. 26.

“Hard to say why, however, I would hypothesize the operators may have been testing or monitoring the rate of infections and realized many workers are on vacation,” AppRiver’s David Pickett notes.

On Dec. 28-29, however, the botnet was highly active. It peaked at 6.5 million messages early morning on Dec. 28, but wasn’t active for long. On the next day, Necurs was observed sending nearly 59 million ransomware messages.

The malicious emails, the security researchers reveal, were masquerading as purchase orders and voicemails, but also claimed to contain images of interest to the intended victims.

Related: Necurs Returns With New Scarab Ransomware Campaign

Related: Necurs Botnet Distributing Locky Ransomware via Fake Invoices

Written By

Ionut Arghire is an international correspondent for SecurityWeek.

Click to comment

Daily Briefing Newsletter

Subscribe to the SecurityWeek Email Briefing to stay informed on the latest threats, trends, and technology, along with insightful columns from industry experts.

Join security experts as they discuss ZTNA’s untapped potential to both reduce cyber risk and empower the business.

Register

Join Microsoft and Finite State for a webinar that will introduce a new strategy for securing the software supply chain.

Register

Expert Insights

Related Content

Cybercrime

The changing nature of what we still generally call ransomware will continue through 2023, driven by three primary conditions.

Cybercrime

A recently disclosed vBulletin vulnerability, which had a zero-day status for roughly two days last week, was exploited in a hacker attack targeting the...

Cloud Security

Cloud security researcher warns that stolen Microsoft signing key was more powerful and not limited to Outlook.com and Exchange Online.

Cybercrime

No one combatting cybercrime knows everything, but everyone in the battle has some intelligence to contribute to the larger knowledge base.

Application Security

Fortinet on Monday issued an emergency patch to cover a severe vulnerability in its FortiOS SSL-VPN product, warning that hackers have already exploited the...

Cloud Security

Microsoft and Proofpoint are warning organizations that use cloud services about a recent consent phishing attack that abused Microsoft’s ‘verified publisher’ status.

Malware & Threats

Threat actors are increasingly abusing Microsoft OneNote documents to deliver malware in both targeted and spray-and-pray campaigns.

Compliance

Government agencies in the United States have made progress in the implementation of the DMARC standard in response to a Department of Homeland Security...