Microsoft says that the number of trojans it has removed from computers around the world in the second half of 2007 rose by 300 percent from the first half. It claims that the software was always there, but software has gotten better at detecting them.

Vinny Gullotto, General Manager of the Microsoft Malware Protection Center, said that the numbers have simply exploded. The most common family of trojans last year was "Win32/Zlob". The majority of trojans come from the United States, China, Russia and South America.

Microsoft said the number of computers around the world that were made safe after being infected with trojans rose from one million in the second half of 2006 to 19 million in the second half of 2007.