Heuristics

Heuristics

Some more sophisticated antivirus software uses heuristic analysis to identify new malware or variants of known malware. Three methods are used: file analysis, file emulation, and generic signatures.^{[citation needed]}

File analysis is the process by which antivirus software will analyze the instructions of a program. Based on the instructions, the software can determine whether or not the program is malicious. For example, if the file contains instructions to delete important system files, the file might be flagged as a virus. While this method is useful for identifying new viruses and variants, it can trigger many false positives.^{[citation needed]}

The second heuristic approach is file emulation, which runs the target file in a virtual system environment, separate from the real system environment. The antivirus software would then log what actions the file takes in the virtual environment. If the actions are found to be damaging or malicious, the file may be marked a virus. But again, this method can trigger false positives.^{[citation needed]}

Another type of heuristics is generic signatures.^{[citation needed]}

Many viruses start as a single infection and through either mutation or refinements by other attackers, can grow into dozens of slightly different strains, called variants. Generic detection refers to the detection and removal of multiple threats using a single virus definition. ^[12]

For example, the Vundo trojan has several family members, depending on the antivirus vendor's classification. Symantec classifies members of the Vundo family into two distinct members, Trojan.Vundo and Trojan.Vundo.B.^[13][14]

While it may be advantageous to identify a specific virus, it can be quicker to detect a virus family through a generic signature or through an inexact match to an existing signature. Virus researchers find common areas that all viruses in a family share uniquely and can thus create a single generic signature. These signatures often contain non-contiguous code, using wildcard characters where differences lie. These wildcards allow the scanner to detect viruses even if they are padded with extra, meaningless code. ^[15] Padded code is used to confuse the scanner so it can't recognize the threat.

A detection that uses this method is said to be "heuristic detection."