Check out for more details: https://www.financemagnates.com/cryptocurrency/news/breaking-etherdelta-might-compromised/
I don't know particularly but the hacker is using some kind of auto transfer script wherein whenever you import your public and private address, all your funds would be transferred to the hacker's address.
But your wallet itself is safe, because you see 'smart contracts' immutable, basically their website domain has been hacked and replaced by the phishing site whenever you navigate to their site, your browser directs you to their phishing site. Hence, that.
When you accessed ED before it was hacked, your wallet is safe. No need to worry. Just have to transfer it.
You can find out more here:
https://www.reddit.com/r/ethtrader/comments/7l46ng/alert_ether_delta_hacked/
Transferring account to MEW:
https://www.reddit.com/r/EtherDelta/comments/6hrxjw/etherdelta_guides_for_first_time_users/dn6heno/