The Sex and the City star has been married to actor Matthew Broderick since 1997 and the couple have three children together.
Relationship expert and 'infidelity analyst' Sarah J Symonds tweeted: 'So now who do these kids looks like? Certainly not like @SJP'
And rather than stay silent, the actress hit back at Symonds, writing:
'Your anonymity doesn't diminish your outrageous and vulgar tweet. And your deletion only reveals your cowardice. @SarahJSymonds'
She continued: 'I'm certain there isn't a woman on this planet who would support your specific kind of cruelty. No apology, no explanation. @SarahJSymonds'
'You should be ashamed @SarahJSymonds. I hope more people join me in voicing their objection to and holding accountable…(cont)
'…uninformed and unkind women like yourself who find pleasure and delight in attacking other women. @SarahJSymonds'
Symonds deleted her unkind tweets (when asked SJP wouldn't confirm what else she had said) soon after being picked up on them.
Parker, who played Carrie in SATC, signed off from the social networking site last night, writing: 'I want to thank everyone for coming to my defense today. I didn't relish the opportunity to publicly reprimand.'