Williams, who has kept quiet about her mysterious relationship with director Spike Jonze, has hired bodyguards to ward off the photographers.
A source told the New York Post, "Before Michelle leaves the house with Matilda, she has a bodyguard go around her block and make sure there are no photographers."
The source added that the security for the Brokeback Mountain actress has gotten considerably tighter.
There were rumours that Williams has been able to get over her breakup with Heath Ledger since she started dating Spike Jonze last month.