posted by Dharmesh

Greetings Messenger fans –

As some of you noticed, we had a problem from Friday night to Saturday morning where our Messenger service was incorrectly blocking some legitimate IP addresses.  We sincerely apologize for any difficulties this caused our users.  And we want to thank those of you that reported this problem to us so that we could quickly fix it.  Because of your help, the incorrect block was only in place for a few hours. 

As you can imagine, we are very serious about our efforts to block virus, malware and other harmful URLs from being passed on to our users.  And we're continually working to improve this process so that we can keep our users safe without having a negative impact on your Messenger service.

There have been some pretty outlandish speculations on what happened so I'd like to give you some facts about our process for trying to block unsafe URLs and about what happened Friday night:

• There are a number of factors that can be used to determine whether a URL is potentially harmful: number of times a URL is sent, the frequency of the URL being sent, the number of accounts the URL is sent from, manually checking the URL, comparing with other "block lists", etc.
• When a URL is deemed harmful, a block can be instated for a specific URL (i.e. www.<domain>.com/<page>) or an entire domain (i.e. *.<domain>.com)
• This entire process for Messenger is managed by a 3rd party that is a Microsoft partner
• On Friday, Microsoft did not request to block any of the URLs that were accidentally blocked
• The blocks were made by our partner as a result of their process to block harmful URLs
• We are still investigating the specific reason our partner made these incorrect blocks and we will work with them to improve their process for detecting harmful URLs while not blocking safe ones

As always, we're open to feedback on how to make Messenger an even greater service.  And again, our apologies to the users that were impacted by this.