vim shows empty block at end of each line

While editing a file in Vim, I tried to do a global search and replace, but I accidentally hit enter after typing this:

:g/$/x

Now Vim is in a funny state where an empty blue box appears at the end of each line, not only in the file I was editing, but in开发者_JAVA技巧 EVERY file I open! I've logged out and back in, but the strange state persists. What happened, and how can I get Vim back to normal?

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It's only highlighting. Type :nohl and it should vanish.