From news.sophos.com
Browser add-ons are a common source of privacy and security concerns. While they are usually legitimate software products with real companies behind them, these plug-ins can also be used by unscrupulous software developers as a way to turn downloads of free software into a revenue stream–dropping browser add-ons that gather information from the user, inject advertisements into websites they visit and even redirect searches and link destinations to the websites of paying customers. They also frequently disguise their installers’ true contents to lure people into allowing them to drop their unwanted payloads.