Critical Description
Google recently created two pdfs with the same sha-1 checksum [1]. There are reports of this breaking svn repositories[2][3].
[1] https://security.googleblog.com/2017/02/announcing-first-sha1-collision.html
[2] https://arstechnica.com/security/2017/02/watershed-sha1-collision-just-broke-the-webkit-repository-others-may-follow/
[3] https://lists.webkit.org/pipermail/webkit-dev/2017-February/028795.html
Additional resources:
https://bugs.webkit.org/show_bug.cgi?id=168774#c23<Paste>
https://shattered.io/