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File verification is a process to determine whether a computer file has been altered in some way. This can occur as a result of corruption, viral intrusion or deliberate activity on the part of a user. For security, it can be important to check on the integrity of a file and to receive an alert if the file changed from an earlier version. There are a number of techniques available for use in file verification.
One option for verifying files is comparing a new file against an older copy, moving through the entire code bit by bit, looking for any changes. Another option involves the use of a checksum. The user creates a block of data from the file and stores this. If the user has doubts about a file, he or she can perform the checksum calculation again and check the new version against the original. If the data is different, the file has changed.
This process can be important in the transmission of data, where users want to identify changes, because that could indicate a problem. A virus might have attached to a file, for instance, or a hacker could have inserted code to track the file or execute a malicious command. In the case of secure, confidential data, changes can indicate the presence of a compromise somewhere in the system that will need to be addressed to keep the data safe. Likewise, users might want to use file verification to confirm the integrity of a backup and make sure that all of the data they will need is there.
Computer programs are available to perform file verification, and most are very fast. When the user executes a command to check on a file, the program can quickly sweep it and return a result. This process might be slower with particularly large files or situations when the program needs to scan each bit of data, rather than using a checksum method. For people exchanging data over a secure connection, the process also includes encrypting and decrypting the data.
There might be cases when file verification can be especially important. In the evaluation of digital evidence in court cases, for instance, all sides want to be assured that the files are valid and have not been altered. A technician who specializes in this process can evaluate the material and determine whether any changes have occurred. This also can be useful in forensic investigation in general, where changes to a file can reveal traces of a criminal trying to cover his or her tracks or deceive investigators.