If my Yahoo! account is compromised, does that affect my Facebook account?
Unfortunately, if you suspect your Yahoo! account has been hacked, the intruder will be able to view all available contact information including info for your Facebook contacts. We recommend that you change your account password.
As a further precaution, we recommend that you scan your computer for viruses and malware whenever this option is available. Following these suggestions will greatly reduce your likelihood of experiencing trouble from computer viruses.
If you believe you have a virus on your system, we recommend that you install an anti-virus program, and contact your computer's user support group for assistance. You can also search the Symantec Virus Encyclopedia.