The paper adds Google (GOOG) discussed buying Square this year, though it's not clear if talks are continuing. Apple and PayPal are said to have held informal talks that never progressed.
Re/code and The Information previously reported Google has shown interest in Square, which processed over $20B worth of transactions last year (largely through its mobile card readers and related apps) and could provide Google with valuable data on offline purchase activity and ad effectiveness (previous). Google's own mobile/offline payments efforts haven't lived up to expectations.
The WSJ's sources state Square had 2013 revenue of $550M, but only with a gross margin of 21% (down from 2012's 27%) after backing out processor payments and other fees. That led net loss to total ~$100M.
Square has been hatching plans to up-sell merchants on value-added software and services, but it remains very dependent on transactions for now. The company has been valued at $5B in private share sales, but public investors might now assign a lower valuation.