Mind Probe and Espionage, Is this spell completely unbalancing? Options

[Runner Smurf]

In the course of running my current campaign, I've run into a serious problem. Espionage/political plots really fall apart when the characters start slinging Mind Probe spells. The more I've thought about it, the more it seems the Mind Probe spell is completely unbalancing - in the game world sense.

For example, intelligence agencies couldn't use field assets - there is simply no way you could ensure that an agent wouldn't be compromised almost immediately. Any organization with any resources at all would make sure that anyone having access to truly secure information would be scanned before being given access.

That being said, is there any way to try and balance the capabilities of the spell? Sure, having a high willpower helps, but it's not going to stop people. Heck, my players have already figured out to hit the target with some drugs first and then scan him.

I've already considered the following limitations:
1. Mind probe cannot search for information - it only allows you access to what they are currently thinking about. Kind of breaks the guidelines listed in the book...
2. Increase the drain?
3. Secondary effects? The link works both ways to an extent, and the caster can pick up personality traits from the target, etc.?

Anybody else have any thoughts or ideas? Am I missing something obvious?

- Runner Smurf