During your analysis, determining the file type of a suspect binary will help you identify the malware's target operating system (Windows, Linux, and so on) and architecture (32-bit or 64-bit platforms). For example, if the suspect binary has a file type of Portable Executable (PE), which is the file format for Windows executable files (.exe, .dll, .sys, .drv, .com, .ocx, and so on), then you can deduce that the file is designed to target the Windows operating system.

Most Windows-based malware are executable files ending with extensions such as .exe, .dll, .sys, and so on. But relying on file extensions alone is not recommended. File extension is not the sole indicator of file type. Attackers use different tricks to hide their file by modifying the file extension and changing its appearance to trick users into executing it. Instead...

Fingerprinting involves generating the cryptographic hash values for the suspect binary based on its file content. The cryptographic hashing algorithms such as MD5, SHA1 or SHA256 are considered the de facto standard for generating file hashes for the malware specimens. The following list outlines the use of cryptographic hashes:

• Identifying a malware specimen based on filename is ineffective because the same malware sample can use different filenames, but the cryptographic hash that is calculated based on the file content will remain the same. Hence, a cryptographic hash for your suspect file serves as a unique identifier throughout the course of analysis.
• During dynamic analysis, when malware is executed, it can copy itself to a different location or drop another piece of malware. Having the cryptographic hash of the sample can help in identifying...

Scanning the suspect binary with multiple anti-virus scanners helps in determining whether malicious code signatures exist for the suspect file. The signature name for a particular file can provide additional information about the file and its capabilities. By visiting the respective antivirus vendor websites or searching for the signature in search engines, you can yield further details about the suspect file. Such information can help in your subsequent investigation and can reduce the analysis time.

VirusTotal (http://www.virustotal.com) is a popular web-based malware scanning service. It allows you to upload a file, which is then scanned...

Strings are ASCII and Unicode-printable sequences of characters embedded within a file. Extracting strings can give clues about the program functionality and indicators associated with a suspect binary. For example, if a malware creates a file, the filename is stored as a string in the binary. Or, if a malware resolves a domain name controlled by the attacker, then the domain name is stored as a string. Strings extracted from the binary can contain references to filenames, URLs, domain names, IP addresses, attack commands, registry keys, and so on. Although strings do not give a clear picture of the purpose and capability of a file, they can give a hint about what malware is capable of doing.

Even though string extraction is an excellent technique to harvest valuable information, often malware authors obfuscate or armor their malware binary. Obfuscation is used by malware authors to protect the inner workings of the malware from security researchers, malware analysts, and reverse engineers. These obfuscation techniques make it difficult to detect/analyze the binary; extracting the strings from such binary results in very fewer strings, and most of the strings are obscured. Malware authors often use programs such as Packers and Cryptors to obfuscate their file to evade detection from security products such as anti-virus and to thwart analysis.

A Packer...

Windows executables must conform to the PE/COFF (Portable Executable/Common Object File Format). The PE file format is used by the Windows executable files (such as .exe, .dll, .sys, .ocx, and .drv) and such files are generally called Portable Executable (PE) files. The PE file is a series of structures and sub-components that contain the information required by the operating system to load it into memory.

When an executable is compiled, it includes a header (PE header), which describes its structure. When the binary is executed, the operating system loader reads the information from the PE header and then loads the binary content from the file into the memory. The PE header contains information such as where the executable needs to be loaded into memory, the address where the execution starts, the list of libraries/functions...

During your malware investigation, when you come across a malware sample, you may want to know whether the malware sample belongs to a particular malware family or if it has characteristics that match with the previously analyzed samples. Comparing the suspect binary with previously analyzed samples or the samples stored in a public or private repository can give an understanding of the malware family, its characteristics, and the similarity with the previously analyzed samples.

While cryptographic hashing (MD5/SHA1/SHA256) is a great technique to detect identical samples, it does not help in identifying similar samples. Very often, malware authors change minute aspects of malware, which changes the hash value completely. The following sections describe some of the techniques that can help in comparing and classifying the suspect binary...