Blake Lively has been targeted with a massive troll campaign amid her legal war with Justin Baldoni … her Instagram profile is flooded with porn.

A source with knowledge tells TMZ … Blake had no idea she had been targeted with the smut … and it’s now gone — her security settings have been updated.

Daniel Roberts, Meta spokesperson, tells us … “This kind of online harassment is wrong and we condemn it. We are removing the content that violates our policies and will continue to monitor for additional violating posts.”

It’s hard to know who started the porn posts – or exactly when, but they began at some point this month … hardly a coincidence amid her polarizing legal battle with Justin … the public taking sides. Worth noting Ryan’s IG was not messed with.

The dozens and dozens of porn posts went under the radar ‘cause they were under the “tagged” section of the app. That’s where anyone – even stars – can be tagged in a photo and it appears in their profile … unless specific settings are in place. Seems Blake with her 45 million followers didn’t have those settings on – but, she hasn’t needed them until now.

As you know … Blake filed a lawsuit against Justin last month — claiming he sexually harassed her on the set of “It Ends With Us” and then tried to ruin her reputation.

Baldoni has fired back at the claims, calling them totally untrue … before filing his own lawsuit against the Hollywood power couple — asking a judge to award him $400 million. He’s also suing the New York Times for a piece they ran after Lively filed her suit.