Something is rotten in Menlo Park. On the public wall slash internal message board thing at Facebook headquarters, modeled on the digital "wall" of the social network, Facebook employees have taken to crossing out the words "Black Lives Matter" and substituting the words "All Lives Matter." That's left CEO Mark Zuckerberg clearly upset. He responded with a private memo obtained by Gizmodo confirming and excoriating the behavior, which he claims will be investigated.

There have been several recent instances of people crossing out "black lives matter" and writing "all lives matter" on the walls at MPK.

Despite my clear communication at Q&A that this was unacceptable, and messages from several other leaders from across the company, this has happened again. I was already very disappointed by this disrespectful behavior before, but after my communication I now consider this malicious as well.

There are specific issues affecting the black community in the Unites States, coming from a history of oppression and racism. 'Black lives matter' doesn't mean other lives don't -- it's simply asking the black community also achieves the justice they deserve.

We've never had rules around what people can write on our walls -- we expect everybody to treat each other with respect. Regardless of the content or location, crossing out something means silencing speech, or that one person's speech is more important than another's. Facebook should be a service and a community where everyone is treated with respect.

This has been a deeply hurtful and tiresome experience for the black community and really the entire Facebook community, and we are now investigating the current incidents.

I hope and encourage people to participate in the Black@ town hall on 3/4 to educate themselves about what the Black Lives Matter movement is about.

According to internal reporting, Facebook has just about two percent black employees. And, in terms of timing, TechCrunch points out that some black students from the Bay Area have a trip to Facebook's HQ planned for tomorrow.

Previously: ISIS Threatens Mark Zuckerberg, Jack Dorsey