Although there are many factors that trigger data corruption, it is often enabled through an external virus stored or installed within the target computer or device. The virus overwrites the original data, modifies the code or permanently deletes it. Besides viruses, data corruption may also occur as a result of hardware or software malfunctions, errors and environmental calamities such as power outages, storms or other disasters. Data can be restored through a backup copy or it can be rebuilt using various data integrity checking algorithms.