Why there are '~(tilde)' in every file's extention when I edited with gVIM?

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http://superuser.com – I'm using gVIM on Windows. Everytime I edit text file and save it, VIM makes a file with '~(tilde)' in extention - like this : 'crappycode.txt~' It's so annoying that I have to delete it manually. Is there any option that stops gVIM to make such file? p.s. sorry for bad english. (HowTos)