Israeli authorities said on Wednesday that they had detected planned cyber attacks against 120 public and private targets in the Jewish state but did not specify the intended victims.
A statement from Israel's National Authority for Cyber Defence said that "in recent days" it had uncovered plans for a mass e-mail attack by what it described as an assailant masquerading as a "legitimate organisation" using a bogus security certificate.
It did not say what countermeasures it had taken but said the attacks threatened "government ministries, public institutions and private individuals".
Haaretz newspaper said that the attackers "tried to exploit a vulnerability in Microsoft Word."
In November two main Israeli TV newscasts were taken over by hackers who beamed an Islamist message threatening divine fire against the Jewish state.
Hackers ostensibly supporting Syrian President Bashar al-Assad posted messages on an Israeli army Twitter account during the 2014 Gaza war and in 2012 hackers disrupted the websites of the Tel Aviv stock exchange and national airline El Al.
Israel is a global player in the cyber-security industry, with about 400 specialist companies.
Its success is partly due to graduates of elite army units who take their electronic warfare skills with them into civilian life at the end of their military service.