The website of Israeli national carrier El Al and that of the Tel Aviv Stock Exchange were both offline on Monday morning just hours after they were reportedly threatened by a Saudi hacker.
Both sites had a temporary message posted which said they had been taken down for "maintenance."
A spokeswoman for the stock exchange confirmed the site had come under attack but said it was only the website and that the trading systems themselves had not been affected.
"There is someone that has been attacking the Tel Aviv Stock Exchange (TASE) website since this morning," Idit Yaaron told AFP, describing what appeared to be a distributed denial of service attack (DDOS).
"The trading systems are okay, there is no problem (with them)," she said.
Earlier on Monday, a hacker who calls himself 0xOmar warned he was going to attack both websites, the Ynet news website reported.
The attack was the latest in a line of incidents over the past two weeks which have seen details of tens of thousands of Israeli-owned credit card details posted online, or Israeli websites defaced by hackers claiming to be from Saudi Arabia or Gaza.