Avast came up with the attached warning which says that:

Another programme on your computer added an extension that may change the way that Chrome works. It can:

-Access your data on all web sites

-Access your tabs and browsing activity

It gives the option to enable the extension or remove it.

Obviously, you do the latter...

Anybody have any more information on this?

Google recently implemented a security change to Chrome that prevents extensions that aren't from the Chrome Web Store from running.

Have you checked your extensions? Anything new, anything missing?

Have you installed or updated ANY software lately? (could be related)

Have you ever downloaded/installed any free software (could contain a malicious back-door)

Would have been easier if you knew the 'name' of the extension that Avast caught.