The S&P 500 and Nasdaq retreated from records to begin the week, finishing with losses for the first session in eight. Energy stocks led losses even as crude oil prices came off of the day's lows. Zynga (ZNGA) - Get Report set a new 52-week high after Piper Jaffray upgraded its stock rating to OVERWEIGHT from NEUTRAL. Analyst Michael Olson said the social game developer was following the same turnaround playbook as Electronic Arts (EA) - Get Report . Atwood Oceanics (ATW) rallied after agreeing to be acquired by Ensco (ESV) in a deal that values the company at a 32% premium to its Friday close. That deal is slated to close in the third quarter. Chipotle (CMG) - Get Report was lower after determining that customers could have been compromised by a cyberattack across 48 U.S. states. The burrito chain had its payment systems hacked between March 24 and April 19.