Data are classified as “dirty” when the database contains errors that render the data inaccurate. This compromises the data integrity. Dirty data may result from human errors in entering data, such as misspelling a name or incorrectly entering an ID number. Dirty data may also result from viruses, worms, or other bugs installed into a system. Hackers may enter a system and alter or remove data. Hardware and software may fail, corrupting or destroying data.