Estimated reading time: 6 minutes
A logic bomb, also called slug code , is a piece of code inserted into an application, virus or malware that implements a malicious function after a certain time limit or under conditions specifications.
These “bombs” are often used via viruses, worms and Trojans to better manage your time and do maximum damage before you are noticed . They perform actions such as corrupting or altering data, reformatting a hard drive, and deleting important files.
In this article I want to explain what a logic bomb is and offer some suggestions for preventing damage.
What is a logic bomb virus?
A logic bomb is often embedded in a virus or otherwise in an executable file. It consists of malicious code that triggers an attack when specific conditions are met. Conditions can be positive (something that happens) or negative (something that doesn’t happen). In the first case an example is that of opening a program, however, an example of a negative condition is a user who does not log in.
Logic bombs are often installed by someone with high level access, such as a sysadmin. Such a person can wreak havoc by setting these codes on multiple systems and programming them to “explode” simultaneously when a certain event occurs. For example, they could trigger when a certain employee is removed from the salary database, ie when he is fired.
The term slag code refers to manipulated code that makes an otherwise safe program malicious. The logic bomb time versions are the most common ones and use the passage of a certain amount of time as a positive condition.
Whatever the name used, the method of attack is clearly the same: the code remains dormant in the infected software until it is triggered . Common attacks involve data corruption, file deletion and hard drive wiping .
How does it work
How a logic bomb works depends on who designed it. Each logic bomb is unique, which is why they are difficult to track . They are usually customized to be as undetectable as possible. They are often disguised to look like a typical computer virus or embedded in other types of malware such as worms . Worms and viruses are different, but logic bombs don’t care about the distinction – they can cause damage through both.
Is a logic bomb actually malware? Since they are part of other programs, no, but they usually have malicious intent. This is why slag codes are so difficult to detect. Furthermore, being “only” code, potentially insertable anywhere, mitigating the risk is more complicated.
The best thing to do, as an end user who might be involved in a logic bomb attack, is to keep an eye out and ask your company’s IT experts to do the necessary checks if in doubt. The risk is to unintentionally trigger the bomb trying to find it.
Examples of attacks
Logic bombs can subtly change a snippet of code so that it appears technically normal to an automated threat detection system, while it would appear highly suspicious to the human eye. In 2016, a freelance programmer voluntarily caused a recurring spreadsheet malfunction at a subsidiary of the Siemens company. The subsidiary continued to hire him to solve the problem he had caused himself (Source). In this case, the employees did not suspect anything until a lucky coincidence forced the malicious code to come out.
Even companies can use logic bombs to hack their customers . In 2005, Sony was embroiled in a scandal for releasing CDs that triggered a logic bomb when inserted into a computer. The slag code contained on the CDs installed a rootkit that blocked the PC’s ability to copy CDs. (Source)
Another high-profile case occurred in the early 2000s, when a UBS Global employee, angered by a salary dispute, planted a logic bomb that caused more than $ 3 million worth of damage . A clear sign that a very small code snippet can cause a great deal of damage. (Source)
In 2013, a time bomb attack in South Korea wiped out the hard drives of several banks and broadcasting companies. The group responsible for the attack put the time bomb inside a piece of malware that ended up infecting over 32,000 systems . The bombs all exploded together, causing chaos across the country. (Source)
Where did they come from and how to prevent logic bombs
As we have also seen in the examples, logic bombs are typically distributed within a closed network, such as that of a company or branch. One of the likely sources is a disgruntled employee with administrator access , so careful monitoring of staff outbound activities should reveal any suspicious activity . But that’s not all, logic bombs can also be placed in email attachments and suspicious file downloads , so users should be vigilant when choosing which files to download.
As we saw when we talked about phishing and social engineering , the most hackable part of a system are often the users. This is why a preventive campaign is always an excellent choice. Taking care of the staff also means offering specific training through ethical phishing services.
In addition to prevention, it’s good to limit administrative privileges to a select group of employees so that someone is less likely to cause serious damage to your network with a logic bomb. This preventative method also reduces the number of suspects in the event of an attack, making belonging to that specific group of employees in itself a deterrent against internal attacks.
The solution proposed by SOD
Where prevention fails and hackers win, it is the ideal field for implementing advanced monitoring and analysis systems.
SOD offers, for example, a SIEM system in the SOC as a Service solution. The SIEM constantly collects information on what is happening in the network . This information is then enriched with contextual metadata to standardize and manage it better. Already this is capable of triggering alarms if some suspicious events occur. But if this were not enough, the SOC also has a “ User and Entity Behavior Analysis ” (UEBA) tool that analyzes user behavior and, thanks to the interaction of an AI, is able to identify suspicious behavior. .
If you want to know more about the SOC service we offer, or if you have any questions about how SOD can help you keep your business safe, don’t hesitate to contact us. We will be happy to answer any questions.
Estimated reading time: 6 minutes
Out of nowhere, someone replies to an email conversation dated months ago. This is a real conversation that actually happened. Maybe it’s about a meeting, a job opportunity. This email seems very relevant, but beware, it could be zombie phishing .
Indeed, something is wrong, the topic discussed has been over for months and now there is a strange error message in the body of the email. This is a sneaky tactic: revive a long dead email conversation.
Not the usual phishing
The Cofense ™ Phishing Defense Center ™ (PDC) spotted a large Zombie Phishing campaign in 2018. The scam , like almost any phishing attack, is carried out through compromised email accounts.
Scammers take over an email account and respond to long-closed conversations with a phishing link or malicious attachment (e.g. malware or a keylogger ) . Since the email subject is usually relevant to the victim, a curiosity-driven click is very likely to occur . In fact, let’s not forget that the original conversation was already present in the messages received, it is easy to think that it is a follow up or similar.
These Zombie Phishing attacks appear to use automatically generated infection URLs to evade detection. No two links are alike, and they are hidden behind “error” messages without too many frills in the body of the message. This scenario provides a pattern of apparent legitimacy for the users who are victims.
The zombies in computer science
In the computer industry, a zombie is a compromised computer connected to the network. The compromised state could be due to a hacker, virus, malware, or trojan horse .
The infected machine performs malicious tasks under a remote direction. Zombie computer botnets are often used to spread email spam and launch denial-of-service (DoS) attacks.
Types of attack
Here are some observed patterns of Zombie Phishing carrying malicious links . A distinguishing factor was the use of two distinct graphic templates containing button or link error messages.
The message reads something like “Incomplete message” or “Inability to show the whole message”. The link or button invites you to click to see the original message. Obviously the click only involves the installation of a malware or other similar events . Note that no two identical links have been identified, a sign that probably a bot was generating the addresses.
Another common factor is the use of domains with the
.icu TLD. This is probably a factor that varies considerably over time. Here are some of the domains found in the first analysis of 2018:
These zombie phish attacks have been observed to use official organizational logos to add legitimacy to the fake login pages. A common practice in phishing techniques that we have already seen in other articles.
Landing pages are designed to look like a legitimate online portal, including a company logo and even a favicon. In these cases the ultimate goal is the theft of the victim’s credentials .
Furthermore, any victim who visits the malicious website is “tagged” using the host’s IP address as an identifier and, after entering the credentials, is directed to the same spam website seen by other victims. This is often done via obfuscated links using URL shorteners (such as
If the same host tries to visit the phishing link again, the fake login page is skipped and you are forwarded directly to the spam page. This markup and URL shortener obfuscation helps attackers keep a low profile and continue their campaign unabated.
The conversation hijacking tactic is by no means new and is now living a new life with zombie phishing . Scammers have hijacked compromised email accounts to distribute malware and phishing emails as replies to conversations that have been concluded for years now.
This technique is still popular because it makes victims much more likely to click on links and download or open files. The threshold of attention against classic phishing attacks is lowered when messages are brought into conversations already in their inbox .
A couple of years old example of this was the botnet Geodo . Basically it is insertion into existing email threads ( conversation hijacking ) to deliver malicious documents. These, in turn, download a sample of Geodo or other malware such as Ursnif , which according to Key4Biz was the most widespread in Italy in June 2020.
However, the effectiveness of this tactic can greatly depend on the content of the conversations . A reply to an automated advertising email is less likely to cause an infection than a reply to a help-desk support thread.
There have been several Geodo zombie phishing campaigns consisting of replies to automated advertising emails. This is an indication that, in some cases, campaigns consist of indiscriminate replies to all emails in a mailbox. Since the volume of these conversation hijacking is still relatively low, the small reach of these emails is probably limited by the number of ongoing conversations .
Certain account types are therefore more likely to attract the direct attention of threat actors and induce them to invest additional effort and time in developing unique phishing campaigns for those accounts.
Defense from zombie-phishing
Here are some quick tips to avoid losing your credentials in a Zombie Phishing attack:
- Beware of email subjects that may seem relevant but come from old conversations
- Beware of any error message in the body of the message
- Don’t trust attached documents just because they’re replying to a conversation
- Hover your mouse over buttons or links in suspicious messages to check for suspicious domains
It has been observed that these campaigns have gotten smarter . To combat this and other forms of phishing, employee training is key.
A properly trained workforce is what it takes to defend your organization against Zombie Phishing attacks.
SOD offers a full service in this regard . We begin by attacking the company in a controlled manner, testing any weaknesses in employee safety or behavior. Subsequently, specific training is designed to remedy the gaps and fully train the staff.
To keep defenses high, our SOCaaS includes the analysis of user behavior, logs of connected machines and the network in a to immediately identify phishing attempts.
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