The virus count rose to "unprecedented levels" in the second half of 2005, increasing from 110,000 to 150,000 by the end of the year, according to F-Secure's half yearly security report.

However, the trend towards mass assaults using network worms dropped significantly.

There were only two major outbreaks: Zotob which caused large disruptions internationally in September; and Sober.Y which flooded email systems in late November. Earlier this year the Zafi.D worm also made headlines.

F-Secure said that the latter part of the year has been defined by the Sony BMG rootkit scandal, along with phishing attacks and the growth of mobile malware.

In November, F-Secure detected the use of rootkit technology in the digital rights management software used by Sony BMG. This led to millions of CDs being withdrawn from distribution.

2005 was characterised by a spate of criminal phishing attempts either directly to online banking customers yielding high profits to the malware authors, or by exploiting man-made and natural disasters.

The number of mobile malware incidents exceeded the 100 mark for the first time, growing proof that the criminal bodies behind their creation are serious in their attempts to exploit this new arena.

The F-Secure report can be seen here.