Yahoo on Monday officially opened the flood gates to allow users to claim a more desirable username that was once owned by someone else. Users have from now until August 7 to request their top five choices for a new Yahoo ID according to a blog post on the subject.

In the event your top choice isn’t available, Yahoo will try one of your backups and so on. The company said they will send out an e-mail in mid-August informing users which of their selections are available with a link to claim it. You’ll need to act fast though as the link is only valid for 48 hours.

Yahoo made headlines back in June when it was revealed they would be resetting and re-issuing inactive IDs. Any Yahoo ID that had been inactive for more than a year would be wiped and made available once again. It’s a decision that will give millions the opportunity to score a more refined and desirable Yahoo ID, but at what cost?

It wasn’t long before critics of the idea voiced their concern over security. Would it be possible to access information belonging to the former owner of your new Yahoo ID? Or perhaps you could send a password reset request to said address at a number of top web destinations and see if anything turns up.

Yahoo said they were confident in their ability to reissue usernames without any security issues and today, they’ve outlined one measure they are taking in partnership with Facebook to protect the previous owner’s privacy. By using a “require-recipient-valid-since” header for incoming password reset requests, Yahoo said they will be able to check the age of the account before the mail is delivered.

If the age of the account is shown to be older than the date of ownership change, the message won’t be delivered and will bounce back to Facebook. This is just how the social network will handle the issue – others will have their own rules for determining account age requirements, Yahoo notes.