Abstract: A theft prevention enclosure system may include a theft prevention structure defining a security region sized to receive an automated teller machine (ATM) therein; a sleeve disposed on the theft prevention structure; and a locking element. The sleeve and the theft prevention structure may together define an enclosed space that extends from the security region. The sleeve may be slidably engaged with the theft prevention structure such that movement of the sleeve relative to the theft prevention structure changes a volume of the enclosed space. The sleeve, when slidably positioned to be positioned against a wall of a structure behind the ATM, may limit or prevent access to a rear side of the ATM. The locking element may be configured to secure the sleeve in position with respect to the theft prevention structure.