Omniboxes or omniboxes.com is a browser hijacker that takes control of your web browser, changing the search engine and homepage. Omniboxes infect your system when you install free softwares downloaded from third party websites. Most users don't read TOS and inadvertently allow the installation of suspicious softwares.
Software vendors who distribute this program earn money for each successful installation.
Uninstallation via Control Panel
For Windows Vista/Seven/8/8.1:
Open the Control Panel >Programs and Features (or Uninstall a program)
AdwCleaner is a free but very powerful software that can remove most spywares, malwares or adwares.
Download and install AdwCleaner: AdwCleaner (by Xplode).
Launch the program and click on Scan.
Remove detected items.
Protect your PC with Malwarebytes Anti-Malware
Malwarebytes Anti-Malware can help you to protect your system against most threats. This software can warn you of potential threat when installing new software (full version only). In its free version Malwarebytes Anti-Malware can clean your system from malwares.