 Mercury Systems Inc. MRCY, -0.91 said Tuesday that it has adopted a one-year shareholder rights plan, also known as a poison pill, as protection from a hostile takeover during a period in which the aerospace and defense technologies company believes its stock is undervalued. The stock, which were indicated up nearly 4 in premarket trading, has tumbled 37.1 year to date, while the SP 500 SPX, 1.38 has rallied 27.6 this year. 