Like most art exhibitions, the great majority of hacks are temporary installations; most are removed within a day or so by MIT Physical Plant, the MIT Confined Space Rescue Team (CSRT), or occasionally by the hackers themselves. It is a traditional courtesy to leave a note or even engineering drawings behind, as an aid to safe de-installation of a hack. Sometimes, the hacks have been de-installed so quickly that members of the MIT community and the general public have had little opportunity to view them. On very rare occasions, community protests have caused the MIT administration to quietly allow a hack to be re-installed and left for a proper viewing interval. The results of certain hacks (often wall murals) have been considered "permanent improvements" to the campus environment, and have been left in place indefinitely, most notably the "Smoot marks" on the Harvard Bridge. The MIT Museum maintains an extensive collection of original hacker artifacts and documentation, and displays some larger items semi-permanently in the Stata Center.