Hitzlsperger, having been without a club since leaving Wolfsburg last summer, signed a short-term contract with the Toffees in October that saw him through to this month.
The 30-year-old former Aston Villa and West Ham player has made seven appearances for the Merseyside outfit so far.
Asked about Hitzlsperger's future, Moyes said: "We have decided to keep him on. Thomas is going to stay until the end of the season."
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