Small and Medium Businesses (SMBs) are increasingly becoming the target of cyber attacks, with 36% of attacks recorded during the last six months aimed at organisations with fewer than 250 employees, according to a new report by Symantec.

That figure was just 18% at the end of December 2011, Symantec said.

During the first half of the year, the total number of daily targeted attacks aimed at SMBs increased at a minimum rate of 24% with an average of 151 targeted attacks being blocked each day during May and June, the report revealed.

According to the June 2012 Symantec Intelligence Report, SMBs faced about 58 targeted attacks per day during the past six months.

Large enterprises consisting of more than 2,500 employees are still facing a high number of attacks, at 69 per day.

Symantec Cyber Security Intelligence manager Paul Wood said it appears to be a direct correlation between the rise in attacks against smaller businesses and a drop in attacks against larger ones.

"It almost seems attackers are diverting their resources directly from the one group to the other," Wood said.

The most targeted sector is the Defence industry, a sub category of the Public Sector, with an average of 7.3 attacks per day.

The chemical and pharmaceutical firms were two other leading prime targets with one in every five targets are directed towards these sectors while manufacturing still accounts for almost 10% of all targeted attacks.

"Targeted attacks use customised malware and refined targeted social engineering to gain unauthorised access to sensitive information. We regard this as the next evolution of social engineering, where victims are researched in advance and specifically targeted," Wood added.

In June, the global ratio of spam in email traffic fell by 1.0% since May, to 66.8% (1 in 1.5 emails). Hungary was the most spammed geography in June, with a spam rate of 74.3% followed by US with 66.4% and UK with 67.2%.

Spam rate for small to medium sized businesses was 66.4%, compared with 66.9% for large enterprises (2,500+), Symantec reports.

The global phishing rate increased by 0.04% in June, taking the global average rate to one in 467.6 emails (0.21%) that comprised some form of phishing attack.

The Netherlands was the country most targeted in June, with one in 54.4 emails identified as phishing attacks.

Phishing attacks targeting SMBs accounted for one in 401.6 emails, compared with one in 402.9 for large enterprises.

The global ratio of email-borne viruses in email traffic was one in 316.5 emails (0.31%) in June, an increase of 0.04% since May.

In June, 27.4% of email-borne malware contained links to malicious web sites, 1.2% lower than May.

Malicious email-borne attacks destined for SMBs accounted for one in 360.8 emails, compared with one in 269.0 for large enterprises.

The Netherlands was the geography with the highest ratio of malicious email activity in June, with one in 48.6 emails identified as malicious, according to the report.

In June, Symantec Intelligence identified an average of 2,106 web sites each day harboring malware and other unwanted programmes including spyware and adware, a decrease of 51.7% since May.

The most frequently blocked malware for the last month was WS.Trojan.H. WS.Trojan.H is a generic, cloud-based, heuristic detection for files that possess characteristics of an as-yet unclassified threat.