A method implemented on a user device (no) that supports multiple user accounts for multiple users, the user device comprising a data storage device storing multiple application profiles for the multiple users, the method comprising: executing a predecessor version of a computer application in a primary user account of the multiple user accounts for the multiple users, wherein the primary user account stores a primary file name in a primary data storage location referencing the predecessor version , the primary file name being a hard link to the predecessor version , wherein the data storage device stores the predecessor version in a predecessor location and the predecessor version is immutable unless changed by an administrator account ; installing , in the primary user account , a user successor version of the computer application on a user account level, comprising: placing the user successor version of the computer application in a clean user successor data storage location , wherein the clean user successor data storage location is a data storage location associated with the primary user account that does not currently have a version of the computer application stored at that location or in which a version of the computer application was present and then conventionally erased; and overwriting the primary file name to be a hard link to the user successor version ; and executing the user successor version of the computer application in the primary user account while a secondary user account of the multiple user accounts maintains a hard link to the predecessor version . executing a predecessor version of a computer application in a primary user account of the multiple user accounts for the multiple users, wherein the primary user account stores a primary file name in a primary data storage location referencing the predecessor version , the primary file name being a hard link to the predecessor version , wherein the data storage device stores the predecessor version in a predecessor location and the predecessor version is immutable unless changed by an administrator account ; installing , in the primary user account , a user successor version of the computer application on a user account level, comprising: placing the user successor version of the computer application in a clean user successor data storage location , wherein the clean user successor data storage location is a data storage location associated with the primary user account that does not currently have a version of the computer application stored at that location or in which a version of the computer application was present and then conventionally erased; and overwriting the primary file name to be a hard link to the user successor version ; and placing the user successor version of the computer application in a clean user successor data storage location , wherein the clean user successor data storage location is a data storage location associated with the primary user account that does not currently have a version of the computer application stored at that location or in which a version of the computer application was present and then conventionally erased; and overwriting the primary file name to be a hard link to the user successor version ; and executing the user successor version of the computer application in the primary user account while a secondary user account of the multiple user accounts maintains a hard link to the predecessor version . <EOS>