Hackers have taken the websites of El Al, Israel's national airline, and the Tel Aviv Stock Exchange offline.
The cyber attack came hours after the companies received a threat from a Saudi computer hacker.
A message was posted on the home page for the Tel Aviv stock exchange on Monday saying that the site has been taken down for "maintenance". It also came up as "too busy".
The BBC reports several Israeli websites have been targeted over the last two weeks.
The El Al website directly referred to "Saudi hacker activity" causing possible disruption online. "El Al is aware that for the past two weeks cyber war rages against Israel" it says.
Israeli media earlier reported that a hacker who describes himself as a Saudi, called OxOmar, had announced plans to make further attacks.
YNet news website said it was informed by the hacker that they would be carried out by a pro-Palestinian group referring to themselves as "Nightmare".
On Sunday, Hamas again praised the hacking of Israeli websites and called for it to be stepped up.
Israeli officials confirmed that at least 20,000 active credit card accounts were affected by a cyber attack at the start of the year.
Banks had to cancel cards and issue new ones after data was published on the internet.
Hackers have warned of the dangers of a so-called cyber war in the Middle East.
However, the BBC reports Israeli computer experts say politically-motivated attacks have taken place for decades. They suggest the latest attacks show the need for the private sector to improve its security.