|Image courtesy of www.facebook.com|
It's usually installed silently during some software installation (usually free software, like Anti-Viruses, free downloaders, etc.), and it's automatically added to your browser extensions.
You may find it and delete it by going to your browser's extension page (Tools->Extensions for Chrome, Tools->Add-ons for Firefox). If you see an extension with weird name, just uninstall it, restart your browser, and the ads should be gone.
The normal ads however, can be removed with AdBlock.
Many advertising companies nowadays use 'tricks' to attract as many customers as possible. You can check out some of their techniques (for example tapping into new senses) on the following link: