The group behind the suspected Russian attack into U.S. government agencies and private companies was able to hack into Microsoft's internal systems and access some of the company's source code, the tech giant said in a blog post on Thursday. Microsoft had previously said it was among thousands of companies that discovered malware on its systems after downloading a routine software update from the company SolarWinds containing a possible "backdoor" for hackers to gain access to sensitive company data. But the admission on Thursday is the first time Microsoft acknowledged that the attackers had successfully broken into the company's systems...