Jared Leto and Mark Ruffalo are masters of disguise at NY Comic-Con

If you were at Comic-Con in New York City over the weekend, you may have passed by Mark Ruffalo and Jared Leto without even knowing it.

The actors went to great lengths to go unrecognized at the event by wearing elaborate masks.

WATCH: Jared Leto Is Terrifying in Full Costume on Suicide Squad

Leto donned a four-eyed monster mask and thought it would be fun to pose with fans who were dressed like characters from his upcoming film, Suicide Squad. "They had no idea," he captioned the pics.

The actor, who plays the Joker in the highly anticipated DC Comics movie,posed with a Harley Quinn lookalike and a guy dressed up as the Joker. "He had no idea," Leto tweeted.

Meanwhile, the Incredible Hulk was also roaming the streets. Ruffalo chose a creepy old man mask to cover up his identity. "Go to hide out and enjoy," The Avengers star Instagrammed.

Ruffalo also snapped selfies with other event attendees. "Had a great time at #comiccon2015 NYC!" he wrote. "Thanks Comic-Con for the Hospitality."

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Masked celebrities at such events is quickly becoming a trend. The Hunger Games star Jennifer Lawrence revealed to ET at San Diego's Comic-Con that her co-star, Josh Hutcherson, was walking around the event with a mask, and later used it to scare her.

WATCH: Justin Bieber Licks Knife, Wears Clown Mask in Crazy Photo Shoot

"He burst into my room and scared the life out of me," she exclaimed.

This all goes to show, you never know who's behind those masks at Comic-Con.