The aftermath of the Rustock botnet takedown, global spam volumes continued to fall and decreased by 6.4 percentage points since March to 72.9% in April while shortened URLs have become increasingly popular recently, being used to lure people to click on advertising links; a practice known as click-fraud, according to a new report by Symantec.

In April, 1 in 168.6 emails contained malware and targeted attacks accounted for approximately 0.02 percent of these. This represents an increase of 10.5% over a period of six months.

The report revealed that the Advanced Persistent Threats (APTs), targeted attacks are frequently delivered by email and designed to breach a specific target for the purpose of industrial espionage.

During April, 11 automated bots were identified to be operating on a popular micro-blogging service, posting messages containing shortened URLs and using a variety of techniques to bring these messages to the attention of other users.

People clicking on these links are redirected to web sites containing advertising links, which in turn will generate pay-per-click revenue for those sites hosting the banner ads.

The report revealed that in April 2011,the global ratio of email-borne viruses in email traffic from new and previously unknown bad sources was one in 168.6 emails (0.593%), an increase of 0.114 percentage points since March.

The most frequently blocked malware targeting endpoint devices for the last month was the W32.Sality.AE virus. This virus spreads by infecting executable files and attempts to download potentially malicious files from the Internet.

In April, phishing activity was 1 in 242.2 emails (0.413%), an increase of 0.02 percentage points since March; analysis of web security activity shows that an average of 2, websites each day were harboring malware and other potentially unwanted programs including spyware and adware, a decrease of 18.2% since March 2011.

Further, 33% of malicious domains blocked were new in April, a decrease of 4.0 percentage points since March while 22.5% of all web-based malware blocked was new in April, a decrease of 1.9 percentage points since last month.

Geographically, Oman became the most spammed in April with a spam rate of 81.9%; in US 72.8% of email was spam and 72.7% in Canada and the UK; spam levels in Hong Kong reached 72.4% and 70.3% in Singapore.