Currently, the most common form of malicious file type attachments are zip files, owing to the large scale of this latest threat. Zip files are a common file format and have often been used for sending malware in the past. There is no indication that a zip file attachment represents an increased likelihood of a file being malicious; however, most businesses are unlikely to use zip files as part of their typical e-mail correspondence.
According to MessageLabs, spam originating from the Bredolab Trojan has steadily increased in recent months, reaching its highest level this month. It currently accounts for 3.5 percent of all spam and 5.6 percent of all malware intercepted each day. So far in October, approximately 3.6 billion Bredolab malware e-mails are likely to be in circulation worldwide each day.