Check out which companies are making headlines after the bell Monday:
Allergan - Sources told CNBC activist investor William Ackman and Valeant Pharmaceuticals were teaming up to pursue a takeover of the specialty health care company. Shares of Allergan and Valeant rallied in after-hours trade.
Facebook - Credit Suisse upgraded the social networking site to outperform from neutral. Shares gained in after-hours trade.
Netflix - The online provider of subscription entertainment reported first-quarter earnings per share of 86 cents on $1.27 billion in revenue, versus expectations of EPS of 83 cents on $1.266 billion in sales. Its shares rose in after-hours trade.