In GFS, most files are modified by appending new data and not overwriting existing data. Crypto-shredding is the practice of 'deleting' data by (only) deleting or overwriting the encryption keys. Eraser securely erases data by overwriting it such that the data is irrecoverable. They accomplish this by overwriting unused areas of executable files. The Windows kernel uses Hyper-V to prevent malicious kernel code from overwriting the CFG bitmap. The feature creates a duplicate video to avoid overwriting the original clip. In software engineering, clobbering a file or computer memory is overwriting its contents. The menu does, however, allow the user to "lock" files to prevent overwriting. Specific methods include overwriting, degaussing, encryption, and media destruction. However, hackers have found ways to circumvent this restriction by overwriting the firmware. The service is seen as 'confused' because it was tricked into overwriting its billing file. This is due to the inherently destructive nature of overwriting data on sequential media. Many government and industry standards exist for software-based overwriting that removes the data. This may bring in new data, overwriting evidence. This had the effect of overwriting the currently loaded program.