The 'extremist' group is the Army of Islam, a senior member of which, Mohammed Jamil al-Nemnem, was whacked by Israel earlier this month. Curiously, though the Egyptians have cracked down on the Army of Islam, arresting 20 members, and fingered Mohammed Jamil al-Nemnem, Israel has not notified them of any details of a threat to Israelis. It would seem prudent to heed the warning.
Fire breaks out in Devira Forest, north of Be'er Sheva; four firefighting crews on scene (Haaretz)
from the article: Israel issues severe travel warning: Al-Qaida may attack in Sinai