Executive Summary

  • November 2021 marked the return of Emotet after the botnet was taken down by law enforcement in January 2021.


In this installment of our monthly email threat review, we present an overview of the email-based threats observed in November 2021 and compare them to the previous month’s threats.

The report provides insights into:

Unwanted emails by category

The following table shows the distribution of unwanted emails per category.

Email category %
Rejected 81.00
Spam 13.42
Threat 4.67
AdvThreat 0.88
Content 0.03

The following time histogram shows the email volume per category per day.

Unwanted emails by category


The listed email categories correspond to the email categories listed in the Email Live Tracking of Hornetsecurity’s Control Panel. So our users are already familiar with them. For others, the categories are:

Category Description
Spam These emails are unwanted and are often promotional or fraudulent. The emails are sent simultaneously to a large number of recipients.
Content These emails have an invalid attachment. The administrators define in the Content Control module which attachments are invalid.
Threat These emails contain harmful content, such as malicious attachments or links, or they are sent to commit crimes, such as phishing.
AdvThreat Advanced Threat Protection has detected a threat in these emails. The emails are used for illegal purposes and involve sophisticated technical means that can only be fended off using advanced dynamic procedures.
Rejected Our email server rejects these emails directly during the SMTP dialog because of external characteristics, such as the sender’s identity, and the emails are not analyzed further.

File types used in attacks

The following table shows the distribution of file types used in attacks.

File type (used in malicious emails) %
Archive 28.9
HTML 23.1
PDF 18.1
Excel 12.0
Disk image files 4.9
Other 4.8
Word 3.9
Executable 3.5
Email 0.6
Script file 0.1
Powerpoint 0.1
LNK file 0.0

The following histogram shows the email volume per file type used in attacks per 7 days.

File types used in attacks

Industry Email Threat Index

The following table shows our Industry Email Threat Index calculated based on the number of threat emails compared to each industry’s clean emails received (in median).

Industries Share of threat in threat and clean emails
Research industry 6.0
Manufacturing industry 5.2
Media industry 4.6
Healthcare industry 4.6
Automotive industry 4.3
Education industry 4.2
Utilities 3.9
Mining industry 3.8
Construction industry 3.5
Transport industry 3.5
Financial industry 3.4

The following bar chart visualizes the email-based threat posed to each industry.

Hornetsecurity Industry Email Threat Index


Different (sized) organizations receive a different absolute number of emails. Thus, we calculate the percent share of threat emails from each organization’s threat and clean emails to compare organizations. We then calculate the median of these percent values for all organizations within the same industry to form the industry’s final threat score.

Attack techniques

The following table shows the attack techniques used in attacks.

Attack technique %
Phishing 49.6
Other 31.9
URL 6.8
Extortion 3.9
Executable in archive/disk-image 2.4
Impersonation 2.3
Advance-fee scam 2.2
Maldoc 0.8
LNK 0.0

The following histogram shows the email volume per attack technique used per hour.

Attack techniques

Impersonated company brands and organizations

The following table shows which company brands and organizations our systems detected most in impersonation attacks.

Impersonated brand or organization %
Sparkasse 62.2
Volks- und Raiffeisenbank 11.7
Amazon 4.9
Deutsche Post / DHL 4.0
PayPal 2.1
DocuSign 1.7
UPS 1.4
LinkedIn 1.3
Fedex 1.2

The following histogram shows the email volume for company brands and organizations detected in impersonation attacks per hour.

Impersonated company brands

It clearly shows the continued campaigns against German banks Sparkasse and Volks- und Raiffeisenbank that started at the end of September 2021.

Return of Emotet

On 2021-11-15, computer systems infected with the TrickBot malware started downloading and installing the Emotet malware. Subsequently, the Emotet botnet was rebuilt and sent malspam from its botnet again. We reported this event in a separate blogpost.