A surprsingly large number of those threats were developed in the last year, with 711,912 new pieces of malware coming out in 2007 compared with 125,243 in 2006.
The good news for Linux and OS X users is that most of these threats are targeted at computers running Windows. And the good news for Windows users is that most of these applications are variations of older threats, which means if your anti-virus software is up to date, you should be relatively safe.
Of course, Symantec puts reports like this out there in order to sell its own security software. But there are several excellent free anti-virus suites that will also help protect your computer from most threats.
source : BBC News