Applications folder permission can not set, says "The operation can’t be completed because you don’t have the necessary permission"

1. Leave it as is.

2. This is due to System Integrity Protection.

(134406)

But when I try to change permission of Applications folders everyone section to No access, a pop up menu says "The operation can’t be completed because you don’t have the necessary permission".

Why do you want to change the permissions on your Applications folder?

Frankly, if you do not know how to change the permissions, you probably do not want to change the permissions.

You will be reducing the security on your systems by messing with this.

I wouldn't be change permissions on the application folder. Do you know that applications are hidden folders?

R

The System Integrity Protection is designed to block changes to System owned locations including /Applications. This is new with El Capitan, and just as it is blocking you, it will block those with bogus access to your Mac. Even root privileges cannot override the SIP protections.

You're better off enabling the firewall on your computer or router and checking that unneeded services are turned off in the Sharing pane of System Preferences.

(134408)

Make sure you do not have any remote access services enabled. System Preferences -> Sharing

Change all your passwords on your Mac.

Make sure you do not have a 3rd party access app installed _AND_ running, such as TeamViewer.com (while TeamViewer.com is a very good application, and is very useful for helping friends and relatives remotely, it has also been used by scamers to trick people into letting them have access to their systems). And TeamViewer.com is not the only such utility, so you should be checking for others.

If you think you have been compromised, you should backup your data (twice is always a good idea), do a clean install, do clean installs of all your applications you have besides the OS X installed one, then move your data (not your apps) back from the backups you made.

I recommend that you get a littlesnitch. littlesnitch will track your Web traffic and tell you which applications are sending data from your computer. Be sure to run it awhile because it will trigger a number of alerts. In trail mode, it will run for three hours per boot for a about a month.

http://www.obdev.at/products/littlesnitch/index.html