The Divergent star became obsessed with Lindsay Mills after landing the part in director Oliver Stone's upcoming drama Snowden and she spent hours researching information about her online.

"I did do so much research because I didn't get a chance to meet Lindsay Mills until we were three months filming into a four-month shoot," Shailene explains to WENN. "I felt like such a stalker. If anyone hacks my computer they're gonna see that I've reached back into Lindsay's years until 2010.

"All we had before were her old Twitter posts before Ed Snowden had released all the information (National Security Agency documents). She used to have a blog and I read every single blog post and all of her social media feeds. I saw old Instagram posts and Googled the heck out of all of her photography."

The actress reveals some of the photographer's self-portraits were really telling and helped her understand her personality.

"It's hard to shape someone based on social media, because, as we all know, you can post anything on social media and that's not a direct reflection of who you are."

But Shailene admits she would have traded all the research for a brief meeting with Lindsay, because after the two women did get together, she realised she had left a lot out: "I thought, 'Damn, I wish I had met her sooner', because there were small physical mannerisms I would've liked to incorporate. But at the same time it's nice that there's a separation between the character in the film and who she is in real life because that protects her integrity and her sanity. I think we tried our hardest to capture the essence of her."

Woodley's new film, in which Joseph Gordon-Levitt portrays the titular Snowden, will be released in cinemas next month (Sep16).