The Twitterverse is buzzing with are-they-or-aren't-they-back-together speculation after Rihanna and ex-boyfriend Chris Brown released two tracks on which they both appear.

The two singles were unleashed on the Internet Monday and instantly sparked a virtual backlash, with many accusing Rihanna of condoning domestic violence for working with the man who was convicted of assaulting her.

Brown was sentenced to five years' probation after he admitted to beating Rihanna in 2009 on the night before the Grammy Awards.

While the two have not indicated that they are once again a couple, Brown can be heard singing on a remix of Rihanna's "Birthday Cake," while she appears on a remix of his "Turn Up the Music."

On Monday, Brown tweeted a link to his song, which Rihanna later re-tweeted. She also tweeted the "Birthday Cake" remix.

Brown also sent a tweet with a happy birthday message to Rihanna, who turned 24 on Monday.

Twitter was flooded with messages of both support and derision, with some tweeters saying the two had simply moved on from their earlier tribulations to continue working together.

But many others questioned how Rihanna could associate in any way with Brown, after she explained to Diane Sawyer in an interview that staying with him sent the wrong message to her female fans.

"When I realized that my selfish decision for love could result in some young girl getting killed, I could not be easy with that part. I couldn't be held responsible for telling them, ‘Go back,'" she said.

"Even if Chris never hit me again, who's to say that their boyfriend won't? Who's to say that they won't kill these girls? These are young girls. I just didn't realize what an impact I had on these young girls' lives until that happened."

Some Twitter users dismissed the singles as a publicity stunt, with @GreggyBennett tweeting: "Rihanna and Chris Brown are the two biggest stunt queens in the world. I have no time for either of them."

Others, such as @paulchowdhry, were more direct in their disdain. "Unless Rihanna and Chris Brown's new track is called, ‘If you like it then you shouldn't have put your first on it' I'm not interested."

Another user with the Twitter handle @KP_LD tweeted: "If my ex partner was on probation for battering me I'd definitely release some music with him... #Rihanna"

MTV's music-only online hub called Hive weighed in with a link to its story on the musical collaboration with the message: "Rihanna and Chris Brown might well be casting themselves as the Ike and Tina Turner for the Twitter generation."

The fact that the two have collaborated is the source of most of the shock and outrage. However, the songs' lyrics have also raised eyebrows, particularly the sexually charged tone of "Birthday Cake."

As Brown sings about how "it's been a long time" and he's been "missing your body," he also says he wants to "give it to her in the worst way."

Brown came under fire a week ago after he made his return to the Grammys as a performer and taking home a trophy. Music fans, and even fellow singers, criticized the show's producers for inviting Brown to perform in light of his assault conviction.

Country singer Miranda Lambert tweeted that she didn't get why Brown got to perform twice because "He beat on a girl…".

Brown accused Lambert of "using my name to get publicity" and then strangely told his followers to buy her album.

A couple of days later he hinted at his collaboration with Rihanna with the tweet: "Let them be mad!!!! We make music. Don't like it, don't listen! Turn up the music remix is coming soon too! Guess who's on it?"