Here's one blog post that describes some background of the situation. Here's a blog post from Brian D. Foy talking about '.' being removed from @INC in 5.26.

Also, it's documented in the perldelta for 5.24.1.

And there's also a CVE for this issue too (CVE-2016-1238).

In reply to Re^6: 'do' command is dead? Surely not? by dasgar
in thread 'do' command is dead? Surely not? by ACI

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