An anonymous reader quotes a report from Motherboard: Government hackers were using a previously-unknown vulnerability in Microsoft's .NET Framework, a development platform for building apps, to hack targets and infect them with spyware, according to security firm FireEye. The firm revealed the espionage campaign on Tuesday, on the same day Microsoft patched the vulnerability. According to FireEye, the bug, which until today was a zero-day, was being used by a customer of FinFisher, a company that sells surveillance and hacking technologies to governments around the world. The hackers sent a malicious Word RTF document to a "Russian speaker," according to Ben Read, FireEye's manager of cyber espionage research. The document was programmed to take advantage of the recently-patched vulnerability to install FinSpy, spyware designed by FinFisher. The spyware masqueraded as an image file called "left.jpg," according to FireEye.