As more employees use instant messaging at work in lieu of email, federal antitrust enforcers issued a warning Friday: Companies under investigation must turn over those records. The <-bsp-bb-link state="{"bbHref":"bbg://securities/4131761Z%20US%20Equity","_id":"0000018d-4653-de1f-adbf-47fb16f10000","_type":"0000016b-944a-dc2b-ab6b-d57ba1cc0000"}">Justice Department and <-bsp-bb-link state="{"bbHref":"bbg://securities/13362Z%20US%20Equity","_id":"0000018d-4653-de1f-adbf-47fb16f20000","_type":"00...