Yeah, a beam of anything is asking for a beam-rider to find it. (Doesn't have to be a missile--wake-follower torpedoes are a form of beam-rider. They don't look for a ship, they try to follow a wake until they run under/into a ship. Passive so the enemy doesn't hear your sonar pinging, nor do sonar masking systems have any effect on it. The weakness is such torpedoes are very predictable and can be tricked into going for a towed decoy.)