Could Existing Malware Infect Vista ?

Microsoft has touted Vista as a more secure version of Windows, but on the day of Vista's official launch, a security company has identified malware already in circulation that can infect computers running the OS. Sophos identified three viruses typically spread through e-mail that can infect Vista customers who use a third party Web e-mail client. While Vista's e-mail client stops Stratio-Zip, Netsky-D, and MyDoom-O, the malware slips past Vista's defenses when users receive infected messages through a Web-based e-mail service, Sophos said.

*www.pcworld.com/article/id,128050-c,vistalonghorn/article.html

so who's really responsible for this? the email providers or microsoft ?