Top 10 Malware July 2021

In July 2021, the MS-ISAC observed Agent Tesla and Jupyter’s return to the Top 10. The Top 10 Malware variants comprise 63% of the total malware activity in July 2021, increasing 1% from June 2021. Shlayer is likely to continue its prevalence in the Top 10 Malware for the coming quarter. However, the April patch from Apple addresses a zero-day vulnerability Shlayer used, which is likely affecting its campaign as we continue to see a 13% decrease in infections, from the previous month. Additionally, Shlayer activity decreased due to the summer break in the education sector, which is the SLTT sector using the most Apple products.

Top 10 malware July 2021 past 6 months

top 10 malware July 2021 pie chart

In July 2021, malvertisement accounted for the greatest number of alerts. Malvertisement continues as the top initial infection vector due to Shlayer activity. Activity levels for dropped increased, while activity for malspam, malvertisement, and multiple decreased. Shlayer activity dropped 13% from the previous month likely due to the April patch from Apple affecting its campaign, as well as the education sector taking time off for the summer. The patch fixes a zero-day vulnerability exploited by Shlayer to bypass Apple’s Gatekeeper, File Quarantine, and Notarization security checks. This patch will likely affect Shlayer’s ability to download second-stage malicious payloads, as well as its ability to download its own payload. That said, it might not necessarily stop its initial infection vector as a whole. It is likely that malvertisement will remain the primary infection vector as Shlayer continues its reign.

Top 10 malware July 2021 initial infection vectors

Dropped – Malware delivered by other malware already on the system, an exploit kit, infected third-party software, or manually by a cyber threat actor. Gh0st, Jupyter, and Mirai are examples of dropped malware.

Multiple – Malware that currently favors at least two vectors. Currently, CoinMiner, CryptoWall, and ZeuS are examples of malware utilizing multiple vectors. ZeuS is dropped by other malware, but it is also delivered via malvertisement.

Malspam – Unsolicited emails, which either direct users to malicious web sites or trick users into downloading or opening malware. Examples in the Top 10 Malware using this technique are Agent Tesla, NanoCore, and Ursnif.

Malvertisement – Malware introduced through malicious advertisements. Currently, Shlayer is the only Top 10 Malware using this technique.

Top 10 Malware and IOCs

Below are the Top 10 Malware ranked in order of prevalence. The respective indicators of compromise (IOCs) are provided to aid in detecting and preventing infections from these Top 10 Malware variants. Note: The associated URIs are aligned with malware’s respective domain(s) or IP(s) and increase the likelihood of maliciousness when found together. The URIs alone are not inherently malicious.

1. Shlayer

Shlayer is a downloader and dropper for MacOS malware. It is primarily distributed through malicious websites, hijacked domains, and malvertizing posing as a fake Adobe Flash updater.

All Shlayer domains follow the same pattern . Below area several examples of domains Shlayer uses.


  • api[.]interfacecache[.]com
  • api[.]scalableunit[.]com
  • api[.]typicalconfig[.]com
  • api[.]standartanalog[.]com
  • api[.]fieldenumerator[.]com
  • api[.]practicalsprint[.]com
  • api[.]searchwebsvc[.]com
  • api[.]connectedtask[.]com
  • api[.]navigationbuffer[.]com
  • api[.]windowtask[.]com

2. CoinMiner

CoinMiner is a cryptocurrency miner that uses Windows Management Instrumentation (WMI) and EternalBlue to spread across a network. CoinMiner uses the WMI Standard Event Consumer scripting to execute scripts for persistence. CoinMiner spreads through malspam or is dropped by other malware.

3. Gh0st

Ghost is a RAT used to control infected endpoints. Gh0st is dropped by other malware to create a backdoor into a device that allows an attacker to fully control the infected device.

4. Mirai

Mirai is a malware botnet known to compromise internet of things (IoT) devices in order to conduct large-scale DDoS attacks. Mirai is dropped after an exploit has allowed the attacker to gain access to a machine.

5. NanoCore

NanoCore is a RAT spread via malspam as a malicious Excel XLS spreadsheet. As a RAT, NanoCore can accept commands to download and execute files, visit websites, and add registry keys for persistence.

6. Jupyter

Jupyter is an infostealer that is downloaded by masquerading as legitimate software. Its primarily targets browser data in browsers such as Chrome, Chromium, and Firefox and has full backdoor functionality.

7. CryptoWall

CryptoWall is a ransomware commonly distributed through malspam with malicious ZIP attachments, Java Vulnerabilities, and malicious advertisements. Upon successful infection, CryptoWall will scan the system for drive letters, network shares, and removable drives. CryptoWall runs on both 32-bit and 64-bit systems.

8. ZeuS

ZeuS is a modular banking trojan which uses keystroke logging to compromise victim credentials when the user visits a banking website. Since the release of the ZeuS source code in 2011, many other malware variants have adopted parts of its codebase, which means that events classified as ZeuS may actually be other malware using parts of the ZeuS code

9. Agent Tesla

Agent Tesla is a RAT that exfiltrate credentials, log keystrokes, and capture screenshots from an infected computer.

10. Ursnif

Ursnif, and its variant Dreambot, are banking trojans known for weaponizing documents. Ursnif recently upgraded its web injection attacks to include TLS callbacks in order to obfuscate against anti-malware software. Ursnif collects victim information from login pages and web forms.