A list of the most dangerous commands

With great power, comes great responsibility.

1. rm -rf * - deletes all files and directories. Recursively. Always check that you are
   1. not root
   2. not in the root-directory
2. dd - according to the manpage, dd copies and converts. The problem arises with the fact that it can be used to copy and convert harddisk-partitions blockwise. Great power (harddisk-mirroring and more), but with great reposibility: If you accidently specify the wrong destination, you are in deep trouble!
3. tar - perfect for backups. But take care of where you are and which paths are stored inside the archive, or you can overwrite good, current data with good, outdated data. (That is, if you just want to recover some files from the archive, but unpack the whole bunch to a temporary location. You need to make sure that you really are in that temporary location.