If you were browsing around the web portal Yahoo from Dec 31‚ 2013–Jan 3‚ 2014‚ then your pc might have been infected with a malware from the sites’ advertisements.
Malware was designed to use up the users computing power to mine bitcoins. For what purpose it may serve, malware coders put “E” into effort‚ of making this malware a success. Indeed it is. As some experts note that it may have generated up to $100‚000 a day, put all four days together and you get a huge sum of amount.