Spam e-mails pose a greater risk to computer users than ever before, according to an 18-month-long study conducted by German institute AV-TEST which involved over 500,000 such e-mails.

The study revealed that every third spam e-mail containing an attachment is infected with malware. Other e-mails try to lure users in various ways to visit infected websites. Another fact that emerged from the study is that 25% of all spambots are located in offices.

The institute checked more than half a million spam e-mails that had been classified as such prior to the investigation and found that almost 14,000, or 2.5% of the total number of e-mails analysed, were infected. Of the 550,000 e-mails analysed, 30,000 contained an attachment and more than 10,000 of these attachments were infected with malware.

Some 400,000 e-mails included website URLs along with text, where 1% of the links directed users to infected websites, while the remainder were mostly offering fake or counterfeit products.

The lion’s share of the analysed e-mails with attachments were sent from the United States, but only 15% were actually infected. On the other hand, e-mails with attachments coming from India had an infection rate of 78%, followed by Vietnamese e-mails with a rate of 77%.

Using protection software on your PC can prevent malware from taking control of your computer as anti-spam programs usually identify Trojans and rootkits, the most common tools used by botnet operators, and eliminate the risks.