The Stars said in a statement Sunday that they had "addressed the issue directly" with Seguin. The tweet showed up on his account Saturday and was quickly removed.
Seguin posted an apology on Twitter and said he was temporarily shutting down his account because of "repeated attempts by 'hackers' to try to damage my reputation."
The 21-year-old Seguin was traded to Dallas by Boston on Thursday, just days after Bruins general manager Peter Chiarelli criticized the No. 2 pick in the 2010 draft as needing to be a "better pro."
Dallas made the seven-player deal because it needs centers, and Seguin figures to be on the Stars' first line.