Always use care when signing in on public computers, such as those located in libraries or Internet cafes. Do not click the Remember My ID checkbox when you sign in, and always click Sign Out when you’re done.
What about phishing scams? It’s best to rely on these methods to ensure you’re signing in to a genuine Yahoo! site:

A spoofed, or fraudulent, web address might look something like this:
If you DON'T see the correct address.
If you don't see the correct address, you might have been directed to a spoofed (or fraudulent) web site--one that looks like a Yahoo! page but is designed to fool you into revealing your confidential information.
If you're at all uncertain, do not sign in. Here's the safest method to sign in to Yahoo!: