I think my account has been compromised.My password doesn't work anymore plus people on my contacts list are getting messages which I haven't sent.

Access your E-mail account from a different computer and then try sending the email to your friends. Your computer is probably infected by an automatic E-mail sending virus/malware. Update your anti-virus software and then do a FULL virus scan of your computer. If you don't have an anti-virus software, you should get one. You can get some for free or free trial. Avast and AVG are highly recommended.

T ry visiting Yahoo's account recovery page:
https://edit.yahoo.com/forgotroot/

It should let you access your account even if you've forgotten your login credentials (user name and password) or if your account has been hacked or otherwise compromised.

If that doesn't resolve your issues, please comment with your Yahoo messenger version, your Windows version, any error messages you're receiving, and any other relevant information.

Please leave feedback if this was helpful, thanks.

Try going to Yahoo's account recovery page: https://edit.yahoo.com/forgotroot
That should let you confirm you're username and password are correct or fix issues if your account has been compromised.
If that doesn't solve the issue, please post your Windows version, Yahoo messenger version, any error messages and as much relevant information as possible.
Please leave feedback if this was helpful, Thanks!

Try visiting Yahoo's account recovery page:
https://edit.yahoo.com/forgotroot/

It should let you access your account even if you've forgotten your login credentials (user name and password) or if your account has been hacked or otherwise compromised.

If that doesn't resolve your issues, please comment with your browser version, your Windows version, any error messages you're receiving, and any other relevant information.

Please leave feedback if this was helpful, thanks.

Try visiting Yahoo's account recovery page:
https://edit.yahoo.com/forgotroot/

It should let you access your account even if you've forgotten your login credentials (user name and password) or if your account has been hacked or otherwise compromised.

If that doesn't resolve your issues, please comment with your browser version, your Windows version, any error messages you're receiving, and any other relevant information.

Please leave feedback if this was helpful, thanks.

Try going to Yahoo's account recovery page: https://edit.yahoo.com/forgotroot
That should resolve issues with username and password, and help you login to hacked / compromised accounts.
If this doesn't fix the issue please comment with your browser, your version of Windows, any error messages you're getting and any other relevant information.
Please leave feedback if this was helpful, thanks.

Try going to Yahoo's account recovery page: https://edit.yahoo.com/forgotroot
That should resolve issues with username and password, and help you login to hacked / locked / compromised accounts.
If this doesn't fix the issue please comment with your browser, your version of Windows, any error messages you're getting and any other relevant information.
Please leave feedback if this was helpful, thanks.

Try going to Yahoo's account recovery page: https://edit.yahoo.com/forgotroot
That should resolve issues with username and password, and help you login to hacked / compromised accounts.
If this doesn't fix the issue please comment with any error messages you're getting and any other relevant information.
Please leave feedback if this was helpful, thanks.

Try visiting Yahoo's account recovery page:
https://edit.yahoo.com/forgotroot/

It should let you access your account even if you've forgotten your login credentials (user name and password) or if your account has been hacked or otherwise compromised.

If that doesn't resolve your issues, please comment with your Yahoo messenger version, your Windows version, any error messages you're receiving, and any other relevant information.

Please leave feedback if this was helpful, thanks.

Yes, there's a lot of this happening. If you can still get into your account, change the password, and make it something unusual, not a standard dictionary word which can be easily cracked. Make it a combination of letters and numbers, eg v1de0 instead of video, and a longer password is better.