It tracks the websites your visits and injects JavaScript code that could record your passwords, etc. Apparently this has been known for some time, but the latest version (Dec 18) uses a new way of doing it. It's very unlikely that your system would be compromised (there's only so much that JavaScript can do in the sandbox provided by Chrome), but it wouldn't hurt changing passwords on the important websites you visit.
More info hereEdit: The author claims that this is benign and was only meant for tracking so he can make money from the extension . Also turns out that you can disable this, though it would've been nice if there was a warning when the extension updated or was installed so you can opt-out.
