A computer worm is a type of Trojan that is capable of propagating or replicating itself from one system to another. It can do this in a number of ways. Unlike viruses, worms don’t need a host file to latch onto. After arriving and executing on a target system, it can do a number of malicious tasks, such as dropping other malware, copying itself onto devices physically attached to the affected system, deleting files, and consuming bandwidth.
Trojan is a malware that uses simple social engineering tricks in order to tempt users into running it. It may pretend to be another, legitimate software (spoofing products by using the same icons and names). It may also come bundled with a cracked application or even within a freeware.
Once it is installed on the computer, it performs malicious actions such as backdooring a computer, spying on its user, and doing various types of damage.
Trojans are not likely to spread automatically. They usually stay at the infected host only.
Downloaders and droppers are helper programs for various types of malware such as Trojans and rootkits. Usually they are implemented as scripts (VB, batch) or small applications.
They don’t carry any malicious activities by themselves, but just open a way for attack by downloading/decompressing and installing the core malicious modules. To avoid detection, a dropper may also create noise around the malicious module by downloading/decompressing some harmless files.
Very often, they auto-delete themselves after the goal has been achieved.
The term “rootkit” comes from “root kit,” a package giving the highest privileges in the system. It is used to describe software that allows for stealthy presence of unauthorized functionality in the system. Rootkits modify and intercept typical modules of the environment (OS, or even deeper, bootkits).
Rootkits are used when the attackers need to backdoor a system and preserve unnoticed access as long as possible. In addition, they may register system activity and alter typical behavior in any way desired by the attacker.
Depending on the layer of activity, rootkits can be divided into the following types:
Usermode (Ring 3): the most common and the easiest to implement, it uses relatively simple techniques, such as IAT and inline hooks, to alter behavior of called functions.
Kernelmode (Ring 0): the “real” rootkits start from this layer. They live in a kernel space, altering behavior of kernel-mode functions. A specific variant of kernelmode rootkit that attacks bootloader is called a bootkit.
Hypervisor (Ring -1): running on the lowest level, hypervisor, that is basically a firmware. The kernel of the system infected by this type of a rootkit is not aware that it is not interacting with a real hardware, but with the environment altered by a rootkit.
The rule states that a rootkit running in the lower layer cannot be detected by any rootkit software running in all of the above layers.
Remote Access Trojans are programs that provide the capability to allow covert surveillance or the ability to gain unauthorized access to a victim PC. Remote Access Trojans often mimic similar behaviors of keylogger applications by allowing the automated collection of keystrokes, usernames, passwords, screenshots, browser history, emails, chat lots, etc. Remote Access Trojans differ from keyloggers in that they provide the capability for an attacker to gain unauthorized remote access to the victim machine via specially configured communication protocols which are set up upon initial infection of the victim computer. This backdoor into the victim machine can allow an attacker unfettered access, including the ability to monitor user behavior, change computer settings, browse and copy files, utilize the bandwidth (Internet connection) for possible criminal activity, access connected systems, and more.
Rogue scanners, also known as fake scanners, fake AV, or rogueware, are pieces of code injected into legitimate sites or housed in fake sites. Their social engineering tactic normally involve displaying fictitious security scan results, threat notices, and other deceptive tactics in an effort to manipulate users into purchasing fake security software or licenses in order to remove potential threats that have supposedly infected their systems. Their warnings were deliberately crafted to closely resemble interfaces of legitimate AV or anti-malware software, further increasing the likelihood that users who see them will fall for the ploy. These malware can target and affect PCs and Mac systems alike. In 2011, known names in the security industry have noted the dramatic decline of rogue scanners, both in detection of new variants and search engine results for their solutions.
Rogueware is one of two main classes of scareware. The other is ransomware. Rogue scanners are not as apparent as they used to be several years ago. It is believed that ransomware has completely replaced rogue scanners altogether.
Point-of-sale (POS) malware is software specifically created to steal customer data, particularly from electronic payment cards like debit and credit cards and from POS machines in retail stores. It does this by scraping the temporarily unencrypted card data from the POS’s memory (RAM), writing it to a text file, and then either sending it to an off-site server at a later date or retrieving it remotely. It is believed that criminals behind the proliferation of this type of malware are mainly after data they can sell, not for their own personal use. Although deemed as less sophisticated than your average PC banking Trojan, POS malware can still greatly affect not just card users but also merchants that unknowingly use affected terminals, as they may find themselves caught in a legal mess that could damage their reputation.
POS malware may come in three types: keyloggers, memory dumpers, and network sniffers.
The term info stealer is self-explanatory. This type of malware resides in an infected computer and gathers data in order to send it to the attacker. Typical targets are credentials used in online banking services, social media sites, emails, or FTP accounts.
Info stealers may use many methods of data acquisition. The most common are:
- hooking browsers (and sometimes other applications) and stealing credentials that are typed by the user
- using web injection scripts that are adding extra fields to web forms and submitting information from them to a server owned by the attacker
- form grabbing (finding specific opened windows and stealing their content)
- stealing passwords saved in the system and cookies
Modern info stealers are usually parts of botnets. Sometimes the target of attack and related events are configured remotely by the command sent from the Command and Control server (C&C).
DNS changers/hijackers are Trojans crafted to modify infected systems’ DNS settings without the users’ knowledge or consent. Once the systems are infected and their DNS settings modified, systems use foreign DNS servers set up by the threat actors. Infected systems that attempt to access specific sites are redirected to sites specified by threat actors.