Security experts at Nettitude reported that VoIP infrastructures worldwide are targeted by a growing number of cyber attacks. The experts noticed that cyber attacks against VoIP system often started just a few minutes after a new server went live. 88 percent of VoIP attacks took place outside of regular working hours, when there would typically be no security staff present to monitor the situation. Most of the attacks seem to originate from France, but offensives from Chinese IPs were the most dangerous.”]
Source: http://securityaffairs.co/wordpress/37844/cyber-crime/voip-systems-hacking.html