Automatically Expire User Accounts

Is there a plugin that can automatically delete user accounts that belong to a certain group after X days after registration?

Here’s what I need to happen:

– a user registers for the site (let’s say default user group is ‘subscriber’).
– once registered, the user needs to perform action A (not important). Once done, the user is approved and the admin will manually change the user’s user group to the next level up (let’s say it’s ‘author’).
– however, if a user doesn’t perform action A before X days, the system will automatically delete their account (this is where I need help).

Can anyone suggest a way to accomplish this?

Thanks,

Verne