The first quarter of 2011 was the most active in history for malware, says McAfee.

According to the security firm's Threat Report, six million unique samples of malware were recorded in Q1. McAfee said February 2011 saw the most new malware samples of the quarter, with around 2.75 million recorded. Furthermore, fake anti-virus software also reached its highest levels in more than a year, with 350,000 unique fake-alert samples recorded in March 2011.

The report also revealed Android was the second most popular mobile platform for malware, just behind Symbian. McAfee said the cybercriminals behind the Zeus crimeware toolkit have also directed attacks toward the mobile platform, creating new versions of Zitmo mobile malware for both Symbian and Windows Mobile systems to steal user bank-account information.

The first quarter of 2011 saw spam levels drop to half of what they were a year ago, with 1.5 trillion messages being sent per day, that's three time s the number of legitimate email messages that are sent. McAfee said the takedown of the Rustock botnet had helped reduce spam levels. However, the number of new botnet infections surged towards the end of Q1.

Furthermore, McAfee said there had also been a spike in the amount of malicious websites that lure web users to visit them with the promise of information on high-impact news events such as the Japanese earthquakes. The security firm said an average of 8,600 new malicious sites are popping up every day. While, 50 percent of the top 100 results of each of the daily most popular search terms led to malicious sites, and on average contained more than two malicious links.

"The Q1 Threats Report indicates that it's been a busy start to 2011 for cybercriminals," said Vincent Weafer, senior vice president of McAfee Labs.

"Even though this past quarter once again showed that spam has slowed, it doesn't mean that cybercriminals aren't actively pursuing alternate avenues. We're seeing a lot of emerging threats, such as Android malware and new botnets attempting to take over where Rustock left off, that will have a significant impact on the activity we see quarter after quarter."