My browser's are 'unable to connect' to some websites after upgrading to mavericks.

Question

the message i get is:
Unable to connect
Firefox can't establish a connection to the server at www.adobe.com.
    The site could be temporarily unavailable or too busy. Try again in a few moments.
    If you are unable to load any pages, check your computer's network connection.
    If your computer or network is protected by a firewall or proxy, make sure that Firefox is permitted to access the Web.
this is happening on reliable sites such as www.adobe.com, however, there are other sites that also won't load such as (http://www.adobe.com/products/reader.html), and though it seems specific to adobe. i had a friend try going to the adobe site on a different machine running osx 10.6 and they could load the page fine. i tried firefox and safari and neither will load the page.
i'm running:
os x 10.9.2
processor- 3.06 GHz Intel Core 2 Duo
memory- 8 GB 1067 MHz DDR3
thanks,
rick

Answer 1

You, or someone using your computer, may have hacked the system to redirect queries to certain servers. The file modified is /etc/hosts.
The easiest way to fix the hosts file is to restore it from a backup that predates the modification, or to copy the unmodified file from another Mac. If you can't do that, then do as below.
Back up all data.
If you have more than one user account, you must be logged in as an administrator.
Triple-click anywhere in the line below on this page to select it:
open -e /etc/hosts
Copy the selected text to the Clipboard by pressing the key combination command-C.
Launch the built-in Terminal application in any of the following ways:
☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)
☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.
☞ Open LaunchPad. Click Utilities, then Terminal in the icon grid.
Paste into the Terminal window by pressing command-V. I've tested these instructions only with the Safari web browser. If you use another browser, you may have to press the return key after pasting. A TextEdit window should open. At the top of the window, you should see this:
# Host Database
# localhost is used to configure the loopback interface
# when the system is booting.  Do not change this entry.
127.0.0.1                              localhost
255.255.255.255          broadcasthost
::1                                        localhost
fe80::1%lo0                    localhost
Below that, you'll see some other lines. There should be nothing above the first line "##". If you have any doubt about that, STOP and ask for guidance. Make sure you scroll all the way to the bottom. Scroll bars are hidden by default until you actually start scrolling, so you may not realize that you’re not seeing the whole document.
If the contents of the TextEdit window are as described, close it, then enter the following command in the Terminal window in the same way as before (by copy and paste):
sudo sed -i~ '11,$d' /etc/hosts
This time, you'll be prompted for your login password, which won't be displayed when you type it. If you don’t have a login password, you’ll need to set one before you can run the command. You may get a one-time warning to be careful. Confirm. Quit Terminal.
If you see a message that your username "is not in the sudoers file," then you're not logged in as an administrator. Log in as one and start over.
That will fix the hosts file. There is now a copy of the old hosts file with the name "hosts~" in the same folder as "hosts". You can delete the copy if you wish. Don't delete the file named "hosts".