My mac isnt right anymore ?

Question

Hi Folks,
  I deleted everything off my mac and restored as was going to sell.  Long story short i didnt sell.
So upon opening the mac again i had to restore applications etc which seem to have worked.
Adding things like firefox whichi use to use is causing problems also with safari ?
when opening a page on fire fox i get pop ups,  yet pop up blocker is switched on ?  also pop ups as in adds on pages i always visited but were never there before.
Safari,  im in a forum and sometimes it contains some adult humor and when clicking next page it will go to yahoo server etc ,  but im not using yahoo ??
i feel i have broken what was a great machine and it just doesnt run like i had it before ???  even downloading my pictures again from a saved hard drive they have duplicated ?
Can someone help me please or does my machine need re formating and starting from day one ??  if so how can i do it ?
I have a mid 2011 imac 21.5 inch running on 4gb ram with 500gb hd.   it is using Yosemite but would just like my old trusty mac back to how i had it

Answer 1

You may have installed the "VSearch" trojan. Remove it as follows.
Malware is always changing to get around the defenses against it. These instructions are valid as of now, as far as I know. They won't necessarily be valid in the future. Anyone finding this comment a few days or more after it was posted should look for more recent discussions or start a new one.
Back up all data before proceeding.
Step 1
From the Safari menu bar, select
          Safari ▹ Preferences... ▹ Extensions
Uninstall any extensions you don't know you need, including any that have the word "Spigot," "Trovi," or "Conduit" in the description. If in doubt, uninstall all extensions. Do the equivalent for the Firefox and Chrome browsers, if you use either of those.
Reset the home page and default search engine in all the browsers, if it was changed.
Step 2
Triple-click anywhere in the line below on this page to select it:
/Library/LaunchAgents/com.vsearch.agent.plist
Right-click or control-click the line and select
          Services ▹ Reveal in Finder (or just Reveal)
from the contextual menu.* A folder should open with an item named "com.vsearch.agent.plist" selected. Drag the selected item to the Trash. You may be prompted for your administrator login password.
Repeat with each of these lines:
/Library/LaunchDaemons/com.vsearch.daemon.plist
/Library/LaunchDaemons/com.vsearch.helper.plist
Restart the computer and empty the Trash. Then delete the following items in the same way:
/Library/Application Support/VSearch
/System/Library/Frameworks/VSearch.framework
~/Library/Internet Plug-Ins/ConduitNPAPIPlugin.plugin
Some of these items may be absent, in which case you'll get a message that the file can't be found. Skip that item and go on to the next one.
The problem may have started when you downloaded and ran an application called "MPlayerX." That's the name of a legitimate free movie player, but the name is also used fraudulently to distribute VSearch. If there is an item with that name in the Applications folder, delete it, and if you wish, replace it with the genuine article from mplayerx.org.
This trojan is often found on illegal websites that traffic in pirated content such as movies. If you, or anyone else who uses the computer, visit such sites and follow prompts to install software, you can expect more of the same, and worse, to follow. Never install any software that you downloaded from a bittorrent, or that was downloaded by someone else from an unknown source.
In the Security & Privacy pane of System Preferences, select the General tab. The radio button marked Anywhere  should not be selected. If it is, click the lock icon to unlock the settings, then select one of the other buttons. After that, don't ignore a warning that you are about to run or install an application from an unknown developer.
Then, still in System Preferences, open the App Store or Software Update pane and check the box marked
          Install system data files and security updates
if it's not already checked.
*If you don't see the contextual menu item, copy the selected text to the Clipboard by pressing the key combination  command-C. In the Finder, select
          Go ▹ Go to Folder...
from the menu bar and paste into the box that opens by pressing command-V. You won't see what you pasted because a line break is included. Press return.