The answer is yes.Every thing can be hacked.You have to be careful.My friend met this problem after that he has change his password.
Its nearly Impossible to Hack Yahoo ID or Gmail ID without targeting Your System !! So only if ur at the looser end then you can be hacked ... The only other way you cud be hacked if someone have some resource in Yahoo and with the help of that resource they pay and ask them to reset password !! This is what i had experienced ... so No point of argument on this !!
As already mentioned, spyware on your computer can steal IDs and passwords. Yahoo is undoubtedly much less hackable than most places, but if you use the same password in more than one place, you are in danger. If someone gets your password from spyware, or by hacking a site that is less secure than Yahoo, they can try using it anywhere else you go, or anyplace they think you might go. Don't reuse passwords.
Phising is the most common way used by hackers to hack any account. Just note whenever you login to your account on any site just check it that the url on your address bar is correct like hacker may keep phising pages on URL like yahoo.maillll.com which people think is an link of yahoo only but it actually is of an hacker.If by mistake you login on phissing page then go asap to your actually url and login and change the password.Recently there was an phissing page for Digitalpoint also.
That is why you never should use common names or words as your password. Of course an installed trojan on your pc that activates a keylogger still can harm you, but the most used method by pesky script kiddies still is trying to get inside accounts by using large dictionary text files and auto-log-in tools that keep on trying until they have a hit and land inside. Best thing to prevent you against such guys is by using a password combination of letters and numbers.
I don't know about Yahoo in particular, but a lot of the chat applications that aren't real IRC have cross-site scripting vulnerabilities (XSS) and could be used to steal information. That would include chat apps that use JavaScript or Flash.
ya yahoo acounts are very easy to hack but it was before few months ago.........now they hav made some changes but these are not working properly.....no one need cookies to open it........