In addition, independent testing organization AV-Test found that out of 550,000 emails flagged as spam, 14,000 were infected with malware. AV-Test combed spam samples between August 2011 and February 2013, and found that close to 14,000 of them were infected, about 2.5 percent of all of the emails they studied.
Some 30,000 of the 550,000 messages came with an attachment -- 10,000 of which were malware-laden. Nearly all of the spam messages with ZIP file attachments contained malware. Around 400,000 spam messages included URLs. Close to 1 percent of those links were malicious malware-serving URLs, while the others were traditional spam offers, such as for counterfeit pharmaceuticals. Some 25 percent of spam comes out of the enterprise, according to AV-Test.
A good chunk of spam comes from enterprise environments: "...the amount of spam sent remained extremely consistent from Monday to Friday before reducing to 25 percent at the weekend, namely on Saturday and Sunday," the report says. "The study therefore proves that 25 percent of all spambots are located in offices, where they are switched off at the weekend. The amount of spam sent then increases" on Mondays, according to AV-Test.
Just how much spam do most inboxes see daily? The maximum number was 80,000, and the U.S. by far is the biggest originator of spam with attachments. Interestingly, of 8,500 of those emails, only somewhere around 1,200 were malicious. Spam with attachments coming from India and Vietnam was almost all malware-laden.
The AV-Test report is available here (PDF) for download. Have a comment on this story? Please click "Add Your Comment" below. If you'd like to contact Dark Reading's editors directly, send us a message.