Here's a link to an AMA of one of the developers of a popular Chrome extension that have been approached by malware companies to buy them.
http://www.reddit.com/r/IAmA/comments/1vjj51/i_am_one_of_the_developers_of_a_popular_chrome/
Here is a list of some extensions you should be careful with.
Add to Feedly
AwesomeNewTabPage
ChromeReload
CrxMouse (supposedly anonymized tracking)
Hola Unblocker
HoverZoom? (FWIW the author denies it)
Neat Bookmarks
ScrollToTopButton
SmoothGestures
Smooth Scroll
Translate Selection
Tweet This Page
Webpage Screenshot Capture
Window Resizer
Youtube Ratings Preview (Creator said he declined an offer after popular pressure).
Source:http://www.reddit.com/r/technology/comments/1vir7a/chrome_extensions_are_being_bought_out_by_malware/
I had to change Hola unblocker and HoverZoom after reading this. If you know good alternatives for the other extensions please feel free to post it. HoverZoom ->> Imagus
Hola Unblocker ->> Proxmate, Zenmate, MediaHint.
I know it's hard to monetize on extensions so that's the reason they sell their extensions but It sucks that extensions creators don't give a damn about their users. Until someone comes up with a model to easily monetize on extensions or Google starts to review extensions I don't see a way to fix this ASAP.