Beginning February 13, Gmail users sending a .js file will receive a bounce message explaining why the email was not delivered. For those people who need to send a .js file, Google recommends using a cloud service to handle the transfer.
The increasing use of malicious attachments is logical as these have a better chance of avoiding a computer's defenses.
“Attackers will frequently change their attack methods in order to be less predictable,” Symantec Senior Information Developer Dick O'Brien told SC Media last fall. “We believe WSF files are popular at the moment because attackers believe they're less likely to be flagged by some anti-spam or anti-virus products.”
For security reasons, Google already restricts the use of .exe, .msc. and .bat files.