Advanced Persistent Threats (APTs): What They Are and How to Defend Against Them

Advanced persistent threats (APTs) have drawn increasing attention from researchers, cybersecurity practitioners, and business organizations. This line of sophisticated cyber-attacks was previously limited to security infringements against military agencies by state-sponsored and politically motivated cybercrime rings.

In recent years, however, the scope of APTs has expanded and now encompasses vulnerable business organizations, financial institutions, utility and manufacturing industry, as well as government agencies. These attacks have typically surfaced in the last two decades, owing to the proliferation of internet-connected services operating mission-critical business and technology operations.

This article will explore the key characteristics of APTs, how they operate, and, most importantly, outline essential strategies for prevention and defense.

What are advanced persistent threats?

Advanced persistent threats are cyber adversaries that leverage sophisticated skills, tools, and resources to exploit vulnerabilities across various attack vectors, including cyber, physical, and deceptive methods. These threats aim to infiltrate and gain control over the secure IT systems of targeted organizations.

The primary goal of attackers using APTs is to steal sensitive information and weaken the security defenses of their targets, enabling future attacks.

What sets APTs apart is their persistence — they repeatedly target victims over an extended period, maintain ongoing access to the compromised systems, and interact with the infrastructure to carry out further malicious activities in the future.

APT vs. ATP

Advanced persistent threats (APTs) should not be confused with advanced threat protection (ATP). While APT refers to the threat itself, ATP describes a category of security solutions and technologies aimed at addressing advanced threats. Understanding this distinction is critical for organizations when building their cybersecurity strategies.

Characteristics of advanced persistent threats

APTs are some of the most sophisticated and damaging cyber threats. Here are several characteristics that distinguish them from traditional cyber-attacks:

1. Long-term objectives and persistence: APTs are designed to achieve specific strategic goals over an extended period. Attackers may remain undetected within a target network for months or even years while continuously working toward their objectives.
2. Highly skilled and well-funded threat actors: APTs are orchestrated by highly skilled individuals or groups with significant financial and technical resources, such as nation-states, organized crime groups, or state-sponsored hacking groups.
3. Sophisticated techniques and tools: APT attackers employ advanced methods like zero-day exploits, custom malware, social engineering, and spear-phishing. They may also use encrypted communication channels and other tactics to avoid detection.
4. Targeted at specific organizations or industries: APTs are highly targeted attacks aimed at specific organizations, industries, or governments with valuable information or assets. Attackers carefully select their targets based on strategic value.
5. Masters of stealth: APT attackers aim to remain undetected within the target’s network by using legitimate credentials, blending in with regular network traffic, and erasing traces of their activities.
6. Multi-stage attacks: APTs involve multiple stages, including reconnaissance, exploitation, establishing a foothold, lateral movement, and data exfiltration or operational disruption. Each stage is carefully planned to maximize success and minimize detection risks.

Notorious examples of APTs

Popular early examples of APTs include the 2009 Operation Aurora attack against tech companies and financial institutions, and the 2003-2009 Titan Rain project against government agencies.

Operation Aurora

Operation Aurora, carried out between mid-2009 and December 2009, was a coordinated cyberattack attributed to the Elderwood Group, a China-based APT allegedly linked to the People’s Liberation Army. The attack targeted over 34 organizations, including major tech companies like Google, Adobe, and Juniper Networks, aiming to access sensitive intellectual property, such as source code repositories, which were poorly secured at the time.

The attackers also sought information related to Chinese dissidents, linking the operation to political motives. Google’s public disclosure of the attack in January 2010 sparked diplomatic tensions between the U.S. and China and prompted widespread cybersecurity reforms. The attackers exploited zero-day vulnerabilities in Internet Explorer, prompting global warnings and highlighting the risks of inadequate cybersecurity measures in critical industries.

Titan Rain

Titan Rain, active from 2003 to 2006, was a series of cyber intrusions targeting U.S. government agencies and defense contractors, including NASA, Lockheed Martin, and Sandia National Laboratories. Believed to originate from PLA Unit 61398 in Guangdong, China, the attackers focused on stealing unclassified but sensitive information, such as engineering designs and military infrastructure details.

While no classified data was confirmed stolen, the breaches exposed critical vulnerabilities in U.S. defense systems and created international mistrust, particularly between the U.S., U.K., and China. The sophisticated methods used — such as accessing less-secure systems to target high-value networks — highlighted the involvement of a disciplined and well-coordinated state-sponsored group.

Traditional cyberattacks vs APTs

Unlike traditional cyber-attacks, advanced persistent threats differentiate in the following ways:

Attacker

The malicious actors behind APT attacks are organized cybercrime groups and state-sponsored attackers. These groups are highly organized, determined and equipped with advanced technology resources to execute APT attacks. 

Target

The target of APTs are not individual consumers of an internet service, but specific organizations, groups, and institutions. These targets may have access to sensitive information, resources and capabilities which — under the control of an external malicious actor — presents a high national security risk.

Purpose

Unlike traditional financially motivated cyber-attacks that target unsuspecting Internet users, APTs are intended for long-term and strategic goals. These objectives are usually politically motivated. In fact, the cost of R&D, execution and maintenance of APT attacks may far outweigh any short-term financial advantages. Another important strategic purpose of APTs is to inflict significant financial damages to the victims, forcing them to shut down operations entirely.

Approach

APTs are not single-run attacks, but long-term and repeated attempts to compromise the target systems. The attacks are therefore slow and sustained. Initial cyber intrusions may be designed to serve as a stepping stone for high-profile attacks in the future. The timeline of these attacks runs across months and years.

How APTs work: Stages in an attack

So, how does an APT attack work? These attacks follow a carefully crafted long-term strategy. The resources, financial support and security expertise are available for the long term. The APT attack is conducted in the following stages:

Phase 1: Reconnaissance and weaponization

Attackers gather information about their targets at this stage. Information is gathered from publicly available data sources (a process called Open Source Intelligence or OSINT), collected through surveillance of employees and operations, as well as by compromising user accounts at target organizations using spear-phishing and social engineering techniques.

In many cases, state-sponsored actors can access sensitive target information from government agencies, and by spies installed at target locations with access to sensitive information. An example could be a spy conducting espionage while working at an ISP that serves private contractors offering services to the target organization.

Phase 2: Delivery

APT attacks may involve direct or indirect mechanisms for delivering an attack exploit. Social engineering techniques such as spear phishing are frequently used to deliver a malicious payload directly to a target network. This attack involves tricking the victims into downloading malicious payload on their corporate IT networks, usually by impersonating a trusted source.

Another indirect attack mechanism is the watering hole attack. Similar to a predator waiting around a pond of water in a dry desert, knowing that a prey will eventually reach the water source.

With the watering hole attack, cybercriminals target and compromise the frequently visited websites and services, injecting the malicious payload that is delivered into the networks used by users to access the compromised services.

Phase 3: Initial intrusion

In this stage of the attack, malicious actors aim to stay low on the radar. They may have access to compromised user account credentials, but they only use it for tasks that appear legitimate and authorized by the organization. Target systems are identified, and lateral movement allows the attackers to access more information about the inner workings of the infrastructure as well as the user accounts.

The objective at this stage is to deliver malicious scripts and payload onto target systems, acquire knowledge about the infrastructure, operations and its vulnerabilities, and compromise more user accounts with higher access privileges.

Phase 4: Command and control

Further exploitation occurs by planting a backdoor into the target network. This backdoor connects the target systems with a backend Command and Control (C2) center. C2 silently communicates with systems and services in the target network.

Publicly available tools and legitimate services are used (and compromised) to establish communication. Examples include social networking sites to collect information, Tor Network to host C2 servers anonymously and remote access tools (RATs) to control target systems.

Phase 5: Lateral movement

Once the target systems are compromised and the C2 can establish a secure and anonymous communication link that stays under the radar, malicious actors aim to enhance their controls of the target network. Their new targets are user accounts, services and systems that can access or contain sensitive information, which is available only with higher access privileges.

These user accounts are otherwise heavily guarded, and any unauthorized activity can be quickly detected. Internal reconnaissance helps map the network and collect useful intelligence. More systems may be compromised to harvest sensitive user information. The next objective is to identify digital assets and resources that involve information such as classified documents, proprietary IP and trade secrets, and sensitive customer information.

(Learn how to use Splunk to detect lateral movement.)

Phase 6: Data exfiltration

This stage involves executing the main objective of APT cyber-attack: to exfiltrate sensitive data. This information can expose government agencies to national security risks or reveal trade secrets to competitors. Protecting this information can be a matter of survival to the victim.

Malicious actors may use secure SSL/TLS protocols, use TOR network for anonymity and even encrypt the data to evade detection.

Defending against APTs

Organizations must adopt a proactive, multi-layered approach to cybersecurity. Strategies include:

1. Developing a robust security framework: Implement frameworks like the NIST Cybersecurity Framework or ISO/IEC 27001.
2. Training employees: Conduct regular security awareness training to prevent phishing and social engineering attacks.
3. Network segmentation and access control: Limit attackers' lateral movement by segmenting networks and enforcing strict access controls.
4. Monitoring and detection: Use SIEM systems, AI, and machine learning to detect abnormal network behaviors.
5. Incident response plans: Have a well-defined incident response plan to detect, contain, and remediate APT attacks.
6. Multi-factor authentication and encryption: Secure sensitive systems and data with MFA and strong encryption.

Countermeasures can be simple

Despite the complexity, sophistication and stealth involved in the APTs, countermeasures against these attacks can be as simple as a security awareness training that prevents your users from falling prey to social engineering ploys.

Yes, you will need advanced intrusion detection systems (IDS) and intrusion prevention systems (IPS), risk management strategy, real-time threat detection, monitoring and control systems. But a security-aware user can act as a strong and sufficient first line of defense against advanced persistent threats.