One in 290.1 emails (0.345%) was malicious in February 2011, according to a report from security company Symantec.

The month has become the most prolific time periods both in terms of simultaneous attacks and malware family integration across Zeus (Zbot), Bredolab and SpyEye.

There were at least 40 variants of malware associated with the Bredolab Trojan, accounting for 10.3% of email-borne malware blocked by MessageLabs Intelligence in February.

The report revealed that Bredolab is not dead and techniques previously associated with Bredolab malware have now become more common among other major malware families.

The vast majority of attacks were related to Zeus and SpyEye, many of the attacks share commonalities with the Bredolab Trojan, indicating some of the features associated with Bredolab were being used by Zeus and SpyEye.

In addition, all of these attacks made use of a ZIP archive attachment that contained an executable comprising the malware code.

In February, 1.5% of malware blocked comprised ZIP archive attachments and further analysis revealed that 79.2% of this was connected with the latest wave of Bredolab, Zeus and SpyEye attacks, said the report.

The report also said that malicious executable files have increased in frequency along with PDF files, the most popular file format for malware distribution.

In 2009, approximately 52.6% of targeted attacks used PDF exploits, compared with 65% in 2010, an increase of 12.4%.

Despite a downturn this month, if the trend were to continue as it has over the past year, 76% of targeted malware could be used for PDF-based attacks by mid-2011, Symantec said.

The report said in February 2011, the global ratio of spam in email traffic from new and previously unknown bad sources was 81.3% (1 in 1.23 emails), an increase of 2.7 percentage points since January.

The global ratio of email-borne viruses in email traffic from new and previously unknown bad sources was one in 290.1 emails (0.345%) in February, an increase of .07 percentage points since January.

In February, 63.5% of email-borne malware contained links to malicious websites, a decrease of 1.6 percentage points since January.

Further, phishing activity was 1 in 216.7 emails (0.462%), an increase of 0.22 percentage points since January.

The report also revealed that China became the most spammed in February with a spam rate of 86.2%, and 81.4% of email was spam in the US and Canada; and spam levels in the UK were 81.1%.