A plugin is a piece of software that acts as an add-on to a web browser and gives the browser additional functionality. Plugins can allow a web browser to display additional content it was not originally designed to display.
An example of a plugin is the free Macromedia Flash Player, a plugin that allows the web browser to display animations using the Flash format. As the Web has become more commercial, Flash has become a popular format for displaying ads in web pages. As a result, many web users have been prompted to download the Flash plug in and have it installed on their systems.
Other popular plugins include Quicktime Player (available on the Apple website) and Acrobat Reader (which in addition to being a plugin for the major browsers is also a stand alone application used to display files using the PDF format).http://www.apple.com/quicktime/download/
(The free version should do anything you need)https://get2.adobe.com/reader/
(Used for using/viewing PDF documents)
Most plugins are available as free downloads. To install the plugin, you visit the website of the plugin’s developer (I've included them in this post) and click on a link that will download the installer for the plugin you have selected. You can save the installer to an easy to find location such as the Desktop or a specific folder you have created to organize all of your downloads. Once you have downloaded the installer, you can open it and follow the prompts to install the plugin on your system. You may have to restart your web browser to enable the additional functionality provided by the plugin.If you still get the message after all the below updates, I would not trust that website.
Make sure your flashplayer is up-to-date. Also, beware that some prompts are tricks to lead to malware websites and are NOT real warnings about updates or missing codecs and such.. To update your flashplayer use this direct link:https://get2.adobe.com/flashplayer/
Note there is a checkbox that will also let you try a trial version of McAfee antirvirus. Personally (and arguably, McAfee is about the most bloated, useless program in existence. And yes, uou must pay for it at the end of the trial. I'd suggest you un-check that option before downloadind the newest flashplayer.
You may need to also update java. Here's the proper link:http://java.com/en/
When prompted to download or update anything, go to Google and google the site's URL and if it has been reported as a malicious site. Here is a link to a website with free tools to help keep yourself safe(r):https://zeltser.com/lookup-malicious-websites/
If everything is up-to-date, then chances are good you are being scammed. If you are being asked about a different plugin, see if it tells you what/which plugin it is referring to. I will be happy to check it out for you.
Hope this helps! (ShutUp Buddy? LOL!)