Google have announced that they are blocking Chrome Extensions which are not hosted at the Chrome Web Store.

This is being done as part of a drive to ensure a malware free experience for users.
What this also implies, is that any extension that you already have installed, but is not hosted on the Chrome Web Store, will be automatically disabled. So, this means that extensions installed by software such as an Antivirus will no longer be usable.
This is what Google wrote at their blog,
Malware can change how browsers work by silently installing extensions on your machine that do things like inject ads or track your browsing activity. If you notice strange ads, broken web pages or sluggish browsing after installing some new software or plugins, you could be affected.
This should not be a serious issue, as almost all of Chrome’s popular extensions are available from the Web Store.
Here are a few useful extensions that we like to recommend:
WOT
Adblock Plus
LastPass Password Manager
Xmarks Bookmark Sync
Pocket
If you are using a Chrome Extension that is not available at the Web store, please drop a comment below and share your thoughts.