Microsoft will ask Hotmail users, who have chosen common passwords, to change them as part of an effort to increase the security of its popular webmail service.
The firm will ban the use of passwords such as "123456" and "ilovecats", which can be easily cracked by malicious hackers using trial-and-error techniques.
"This new feature will be rolling out soon, and will prevent you from choosing a very common password when you sign up for an account or when you change your password," the Telegraph quoted Dick Craddock, Microsoft's group program manager for Hotmail, as saying.
"If you're already using a common password, you may, at some point in the future, be asked to change it to a stronger password," he stated.
Apart from tightening its rules on passwords, Microsoft has implemented a feature in Hotmail to allow users to report when a friend's account appears to have been hacked by spammers.
Incoming emails can now be flagged as "My friend's been hacked!" which alerts Hotmail's security systems to a potential breach.
The user whose account sent the email is also asked to change their password so the spammers cannot gain access again.
The firm said alerts would also be shared with Google and Yahoo! when a Hotmail user receives spam from a friend's Gmail or Yahoo! Mail account.