Malspam campaigns are utilizing a new attachment type that is doing a good job in bypassing antivirus and mail filters. These attachments are called Excel Web Query files and when opened will attempt to pull data from external sources. The problem is that the data being imported by the spreadsheet can also contain Excel formulas that launch applications on the computer. These formulas can then be used to launch scripts that download and install malware onto the computer, which is explained later in the article. There have been three spam campaigns utilizing IQY attachments.
Source: https://www.bleepingcomputer.com/news/security/malspam-campaigns-using-iqy-attachments-to-bypass-av-filters-and-install-rats/