An Israeli security source told the Israeli newspaper Yedioth Ahronoth that "on a scale of 1 to 10, the warning was about 3-4. In other words, not really immediate, but still a warning that could not be ignored".
The jet was diverted first to Montreal and then to Hamilton. The 193 passengers were then escorted by police to Toronto and the jet continued its regularly scheduled flight to Los Angeles. The attack was aimed at taking out unidentified Israeli military/government members on that flight. - Adam Geibel
Canadian security officials revealed the details of the threatened terror attack on an Israeli El Al Boeing 767 passenger jet enroute to Pearson airport on the 23rd. While the plane was in the air, Mossad agents in Tel Aviv notified airport and Canadian security agents that Al-Qaeda operatives were planning to attack the descending jet with a surface-to-air rocket from a van or truck on nearby highways. Reports also mentioned that small arms fire would have been directed at the plane while it was on the tarmac (possibly as a backup plan).