Reese Witherspoon says that she likes to "creep around" online to find out what her exes are up to.

The Hollywood star told Cover Media at the London premier of This Means War that she likes to spy on people sometimes.

Her new movie is about two CIA operatives, played by Tom Hardy and Chris Pine, that get into an epic battle with each other after they find out they are dating the same woman, played by Reese.

And starring in the spy-themed action comedy has given the Oscar winner a taste for some detective work, although all in harmless fun.

"Nothing further than your basic cyber-spying," Reese said on how far she goes to check up on people. "Like stalk the high school boyfriend on Facebook, that kind of thing."

"Creep around and look at [pictures of] his kids and go like, Oh my God, his kids are amazing.'"

Reese added that she loved spending time in London as she got to catch up with a close pal.

"Yes, I have a best friend here. So yeah, I love to hang out with her, it's nice," she said.

Reese married Hollywood agent Jim Toth in March last year and revealed that they like to watch the latest films on their date nights.

"Yes, I like to go to the movies," the mother-of-two said. "I recently saw The Descendants and I loved The Artist, so yeah, I love to go to the movies."