Hide plugins you use

You can add any of these lines to your .htaccess files. The directive will affect the Folder that your .htaccess is in and all folders below it.
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Options -Indexes

(this prevents listing of directories)
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Options +Indexes

(this allows listing of directories, possibly useful to override an .htaccess directive stopping listing for all directories in case you want to allow it for particular ones)
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IndexIgnore *

(will prevent listing of all files, the "*" is a wildcard)
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IndexIgnore *.gif *.jpg

(will prevent listing of any files with .gif or .jpg extensions, but will allow other listings)

Also, some folks simply put an index.php or index.html file with a custom message about trying to browse directories

bunch more info
https://www.javascriptkit.com/cgi-bin/search/search.cgi?zoom_query=.htaccess&zoom_per_page=10&zoom_and=1&zoom_sort=0

Also, some folks simply put an index.php … with a custom message about trying to browse directories

dont put an index.php inside your wp-content/plugins directory. Doing so will break your dashboard.

dont put an index.php inside your wp-content/plugins directory

yikes – sorry for that

I have an index.html in mine and that works.

yeah, index.html’s work, its the .php extension that screws stuff up. Ive no idea why, I never looked that hard, i just know it does.

You can take care of this in three places.

A)
If you have access to your httpd.conf (server configuration) file, add the following to the <Directory> section. The IndexIgnore directive adds to the list of files to hide when listing a directory.

IndexIgnore *

B)
If you can edit your .htaccess file (the one in the folder you have problem with, the plugins directory), insert the following:

Options -Indexes

This stops showing directory listings for URLs which map to the directory.

C)
You could also disable dir indexing completely. Find the following line in your httpd.conf and place a # in front of it.

LoadModule autoindex_module modules/mod_autoindex.so

Here is a good page on IndexIgnore: IndexIgnore

Btw, you could also just restrict access to the directory completely with the Allow,Deny directive, but that is another story. See here if interested: Order Allow,Deny