Two weeks ago, vendors were alerting users to a new class of malware, worms, and viruses buried in PDF files. The PDF file format was an effective disguise for executable code and image-based spam. McAfee recently reported an uptick in the use of Excel file formats to carry malware and spam. RAR-compacted archives with spam inside text files are a new vector, McAfee says. Older programs such as Word and Excel “are often harder to keep current,” Symantec warns.”]
Source: https://www.darkreading.com/analytics/file-formats-a-moving-target