How to spot malspam campaigns like "Annual Leave"

Also Known As: Annual Leave malspam campaign
Damage level: Severe

What is "Annual Leave" email virus?

Our malware researchers examined this email and found that it is used by cybercriminals who aim to trick recipients into infecting their computers with FormBook malware. The email itself is disguised as a letter regarding some payment terms. It has a PDF document attached to it that downloads an ISO file that contains malware.

Annual Leave email virus malware-spreading email campaign

More about the "Annual Leave" malspam campaign

This email asks recipients to revise the PI and reconfirm bank details. It requests to confirm payment terms. As we mentioned in the introduction, this email contains a PDF document named "Proforma Invoice 0856132.pdf" (its name may vary). Clicking anywhere on that PDF document when it is opened downloads an ISO file.

That ISO file contains a malicious executable. Double-clicking (executing) that executable infects a computer with FormBook malware. FormBook is an information-stealing malware. It can log keystrokes (record keyboard input), capture screenshots, steal information such as saved login information, clipboard data, banking information, and more.

Also, FormBook can receive commands to download and open files, reboot and shut down a computer, clear browser cookies, run commands via ShellExecute, and more. Thus, FormBook can infect computers with other malware (e.g., ransomware, crypto-mining malware).

Threat Summary:
Name Annual Leave malspam campaign
Threat Type Trojan, password-stealing virus, banking malware, spyware.
Hoax Email attachment is some financial document that needs to be reviewed.
Attachment Proforma Invoice 0856132.pdf (its name may vary)
Detection Names (Proforma Invoice 0856132.pdf) N/A (VirusTotal)
Detection Names (Executable Within ISO File) Avast (Win32:PWSX-gen [Trj]), Combo Cleaner (Gen:Variant.Lazy.267351), ESET-NOD32 (A Variant Of MSIL/TrojanDownloader.Tiny.CBQ), Kaspersky (HEUR:Trojan.MSIL.Scarsi.gen), Microsoft (Trojan:Win32/Leonem), Full List Of Detections (VirusTotal)
Symptoms Trojans are designed to stealthily infiltrate the victim's computer and remain silent, and thus no particular symptoms are clearly visible on an infected machine.
Payload FormBook
Distribution methods Infected email attachments, malicious online advertisements, social engineering, software 'cracks'.
Damage Stolen passwords and banking information, stolen online accounts, identity theft, additional computer infections, and more.
Malware Removal (Windows)

To eliminate possible malware infections, scan your computer with legitimate antivirus software. Our security researchers recommend using Combo Cleaner.
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Malspam campaigns in general

Emails used to trick recipients into infecting computers usually are disguised as important/official/urgent letters from legitimate companies, organizations, or other entities. Cybercriminals include malicious links or attachments in their emails. It is common for files attached to such emails to be disguised as invoices or other financial documents.

Examples of other malspam campaigns are "Concept Design Drawings Email Virus", "Invoices Copies Are Not Clear Email Virus", and "TEXTIMA Export Email Virus".

How did "Annual Leave email virus" infect my computer?

A computer becomes infected with FormBook malware after executing a malicious executable placed in the ISO file that gets downloaded after clicking anything in the PDF document attached to the email. Cybercriminals succeed when users download and execute malware by themselves.

In addition to using PDF documents, ISO files, and executables, threat actors often use MS Office documents, archives (like ZIP and RAR), and JavaScript files to distribute malware. It is important to mention that malicious MS Office documents cannot infect computers until macros commands are enabled (unless they are opened with MS Office released before 2010).

How to avoid installation of malware?

Download software from trustworthy sources such as official websites and stores. Avoid downloads from shady pages, P2P networks, third-party downloaders, free file hosting pages, etc. Do not trust advertisements on suspicious web pages.

Carefully examine emails before clicking links or opening files included in them. Note that irrelevant emails sent from unknown addresses often contain malicious links or files. Keep the operating system and installed software updated. Use reputed antivirus software and run system scans regularly. If you've already opened "Annual Leave email virus" attachment, we recommend running a scan with Combo Cleaner Antivirus for Windows to automatically eliminate infiltrated malware.

Text presented in the "Annual Leave" email letter:

Subject: Review PI Payment Terms - 100% TT in Advance Not Accepted

Good day Sir,

My colleague is currently on annual leave so I will stand-in shortly.

Kindly confirm why your payment terms is 100% advance instead of 30% TT before shipment and 70% Balance TT after shipment.

Please revise the PI and reconfirm bank details as payment is scheduled for next tomorrow 23/11/2022.

Best Regards,

Chen Liu (Mrs)
Manager, Acounts Payables
Datong Coal Mining Group
1510-1512, West Tower, Shun Tak Centre,
168-200 Connaught Road, Central, Hong Kong
Tel : (852) 25458986,Fax : (852) 25458784

Malicious ISO file distributed via PDF document attached to this email:

Malicious ISO file distributed through Annual Leave email  spam campaign

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Quick menu:

Types of malicious emails:

Phishing email icon Phishing Emails

Most commonly, cybercriminals use deceptive emails to trick Internet users into giving away their sensitive private information, for example, login information for various online services, email accounts, or online banking information.

Such attacks are called phishing. In a phishing attack, cybercriminals usually send an email message with some popular service logo (for example, Microsoft, DHL, Amazon, Netflix), create urgency (wrong shipping address, expired password, etc.), and place a link which they hope their potential victims will click on.

After clicking the link presented in such email message, victims are redirected to a fake website that looks identical or extremely similar to the original one. Victims are then asked to enter their password, credit card details, or some other information that gets stolen by cybercriminals.

Email-virus icon Emails with Malicious Attachments

Another popular attack vector is email spam with malicious attachments that infect users' computers with malware. Malicious attachments usually carry trojans that are capable of stealing passwords, banking information, and other sensitive information.

In such attacks, cybercriminals' main goal is to trick their potential victims into opening an infected email attachment. To achieve this goal, email messages usually talk about recently received invoices, faxes, or voice messages.

If a potential victim falls for the lure and opens the attachment, their computers get infected, and cybercriminals can collect a lot of sensitive information.

While it's a more complicated method to steal personal information (spam filters and antivirus programs usually detect such attempts), if successful, cybercriminals can get a much wider array of data and can collect information for a long period of time.

Sextortion email icon Sextortion Emails

This is a type of phishing. In this case, users receive an email claiming that a cybercriminal could access the webcam of the potential victim and has a video recording of one's masturbation.

To get rid of the video, victims are asked to pay a ransom (usually using Bitcoin or another cryptocurrency). Nevertheless, all of these claims are false - users who receive such emails should ignore and delete them.

How to spot a malicious email?

While cyber criminals try to make their lure emails look trustworthy, here are some things that you should look for when trying to spot a phishing email:

  • Check the sender's ("from") email address: Hover your mouse over the "from" address and check if it's legitimate. For example, if you received an email from Microsoft, be sure to check if the email address is @microsoft.com and not something suspicious like @m1crosoft.com, @microsfot.com, @account-security-noreply.com, etc.
  • Check for generic greetings: If the greeting in the email is "Dear user", "Dear @youremail.com", "Dear valued customer", this should raise suspiciousness. Most commonly, companies call you by your name. Lack of this information could signal a phishing attempt.
  • Check the links in the email: Hover your mouse over the link presented in the email, if the link that appears seems suspicious, don't click it. For example, if you received an email from Microsoft and the link in the email shows that it will go to firebasestorage.googleapis.com/v0... you shouldn't trust it. It's best not to click any links in the emails but to visit the company website that sent you the email in the first place.
  • Don't blindly trust email attachments: Most commonly, legitimate companies will ask you to log in to their website and to view any documents there; if you received an email with an attachment, it's a good idea to scan it with an antivirus application. Infected email attachments are a common attack vector used by cybercriminals.

To minimise the risk of opening phishing and malicious emails we recommend using Combo Cleaner Antivirus for Windows

Example of a spam email:

Example of an email spam

What to do if you fell for an email scam?

  • If you clicked on a link in a phishing email and entered your password - be sure to change your password as soon as possible. Usually, cybercriminals collect stolen credentials and then sell them to other groups that use them for malicious purposes. If you change your password in a timely manner, there's a chance that criminals won't have enough time to do any damage.
  • If you entered your credit card information - contact your bank as soon as possible and explain the situation. There's a good chance that you will need to cancel your compromised credit card and get a new one.
  • If you see any signs of identity theft - you should immediately contact the Federal Trade Commission. This institution will collect information about your situation and create a personal recovery plan.
  • If you opened a malicious attachment - your computer is probably infected, you should scan it with a reputable antivirus application. For this purpose, we recommend using Combo Cleaner Antivirus for Windows.
  • Help other Internet users - report phishing emails to Anti-Phishing Working Group, FBI’s Internet Crime Complaint Center, National Fraud Information Center and U.S. Department of Justice.

Frequently Asked Questions (FAQ)

Why did I receive this email?

The same email was sent to all recipients. In most cases, emails used to deliver malware are non-targeted (not personal).

I have downloaded and opened a file attached to this email, is my computer infected?

No, the file (PDF document) attached to this email does not infect computers. Computers become infected after executing an executable within an ISO file that gets downloaded after clicking anywhere in the attached PDF document.

I have read the email but didn't open the attachment, is my computer infected?

It is safe to open emails that contain malicious attachments or links. Computers cannot get infected without opening the contents of emails used to deliver malware.

Will Combo Cleaner remove malware infections that were present in email attachment?

Yes, Combo Cleaner scans the operating system and removes detected malware. It can detect almost all known malware. Typically, high-end malware hides deep in the system. Thus, it is important to run a full system scan to eliminate high-end malware.

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About the author:

Tomas Meskauskas

Tomas Meskauskas - expert security researcher, professional malware analyst.

I am passionate about computer security and technology. I have an experience of over 10 years working in various companies related to computer technical issue solving and Internet security. I have been working as an author and editor for pcrisk.com since 2010. Follow me on Twitter and LinkedIn to stay informed about the latest online security threats. Contact Tomas Meskauskas.

PCrisk security portal is brought by a company RCS LT. Joined forces of security researchers help educate computer users about the latest online security threats. More information about the company RCS LT.

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Malware activity

Global malware activity level today:

Medium threat activity

Increased attack rate of infections detected within the last 24 hours.

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