You can minimise your exposure to viruses by following these simple guidelines:
Never send, click, open, save, or run email attachments that you weren’t expecting. (Be particularly cautious of executable files, which end with the extensions .exe, .com, .vbs, .lnk, .pif, .scr, .bat.)
Back up important files on your computer, just in case originals become corrupted.
If you receive an email attachment from someone you don’t trust, delete the message immediately without opening the attachment. If you know and trust the sender, email the person to verify that they meant to send the attachment.
Make sure any attachments you send are virus-free. Fortunately, Yahoo! Mail automatically scans your outgoing attachments for viruses. Including a description of any attachment you send in the body of your message will let the recipients know the email and the attachments are from you.