Upgrades:
Wal-Mart (WMT) upgraded to Overweight from Equal Weight at Barclays
Downgrades:
Twitter (TWTR) downgraded to Underperform at RBC Capital Mkts; target lowered to $14 from $17
Other:
Twitter (TWTR) initiated with a Hold at Loop Capital; target $18
Facebook (FB) initiated with a Buy at Loop Capital; target $165
UnitedHealth (UNH) initiated with a Buy at Evercore ISI
Amazon (AMZN) target raised to $950 from $855 at Mizuho