Last season, Moyes' Sunderland team were relegated, finishing bottom of the Premier League and he resigned in May, having been sacked by both Real Sociedad and Manchester United before that.
The 54-year-old said it was a simple decision to take over at West Ham, despite only being given a contract to the end of the season, and accepted he will need to rebuild his reputation.
"I thank my coaching team and the staff at the training ground for their support, loyalty and dedication - I have been lucky to have worked with such good people". "Couple of quick meetings and I find myself here now. I had two or three good conversations with Karren". "I am back in, it's what I do". I want to do well, I want the team to do well.
"You can see the turnover of managers at the moment", he said. If I'd taken over at the start of season I'd have said a year at the time. It gives me a chance to look at the club and gives the supporters a chance to see David Moyes working. "This was a really easy decision to make", he said. "We will give them sessions and plenty of them, it'll be tough for them". In that, he is the opposite of the highly personable Bilic and perhaps what West Ham need, having gone so stale.
"My ambition is short term".
"I didn't do enough due diligence at..."
"I have a point to prove. Sometimes you have to fix things and maybe I've got a little bit to fix".
Later in the month, the Hammers travel to face the Gunners in the Carabao Cup quarter-finals.
His first match in charge will be when the Hammers visit Watford on November 19 followed by welcoming Leicester City to the Olympic Stadium on November 24.
"He's a good manager", said Januzaj.