Starboard owns a relatively small slice of Yahoo (a reported 1.7%), but the firm's concerned that its investment might evaporate if the current board, and CEO Marissa Mayer, continue to steer the ship. Yahoo's search and ad sales businesses have struggled to compete with rivals Facebook and Google, and estimates suggest that the company's also facing its largest drop in sales in six years -- a slump of nearly 14 percent.

Meanwhile, Yahoo has been receiving interest from "credible" buyers argues Starboard. Companies such as Time Inc. and Verizon -- the latter which recently bought that other internet stalwart, and Engadget parent company AOL -- have apparently shown interest. Starboard clearly thinks a sale would make most sense (for its interests, at least). Yahoo already ceded to the investment firm (and others) when it reversed a plan to spin off its valuable stock in Alibaba, and it wouldn't be the first time a board change has happened in response to investor pressure.

Yahoo made some bold purchases under Mayer -- such as buying Tumblr -- none of which have been able to reverse its fortunes. It recently shut down all its digital magazines, and shuttered its Games vertical. The move to replace the current directors would still be a few months out, but Starboards track record includes taking out the entire board at Olive Garden's parent company, so the threat is very real.