Brought to you by the letter “X” – Sesame Street’s YouTube channel is back up today after being shut down Sunday when hackers took over the site and replaced the videos with porn.

For about 20 minutes yesterday, visitors to the YouTube channel of the popular children’s show saw hardcore porn instead of Elmo and Big Bird.  The channel has nearly 150,000 subscribers, and usually hosts dozens of clips from the PBS program.

But Sunday, the hackers replaced the page’s banner to read, “SESAME STREET: I’TS [sic] WHERE PORN LIVES.” In the profile description, the hackers wrote: “WHO DOESN’T LOVE PORN KIDS? RIGHT! EVERYONE LOVES IT…PLEASE DON’T LET SESAME STREET TO GET THIS ACCOUNT BACK KIDS …WE GONNA MAKE ALL THE AMERICA HAPPY!”

The banner pinned the hacking on two YouTube users, MrEdxwx and MrSuicider91. MrSuicider91 has yet to comment; MrEdxwx posted a video on his own channel stating, “I did not hack Sesame Street. I am an honsest [sic] youtuber. I work hard to make quality gameplay videos and most important I respect the community guidelines.”

It’s unclear how the hacking happened, and no one has come forward to claim responsibility.

After the hacking, the channel was shut down by YouTube due to “repeated or severe violations of our Community Guidelines” which ban explicit material from the website.

Sesame Workshop, the organization behind Sesame Street, issued an apology after the hacking Sunday, and said in a statement on its YouTube channel:  ”We apologize for any inconvenience our audience may have experienced yesterday…our channel was temporarily compromised, but we have since restored our original line-up.”

A YouTube spokesperson told ABC News that “YouTube’s Community Guidelines prohibit graphic content. As always, we remove inappropriate material as soon as we are made aware of it.”