It doesn't help make your investment case when one of the most ruthless and powerful tech companies in the world is after you.

But that seems to be what's happening with Adobe Systems (ADBE), which is certainly feeling the heat of Apple's (AAPL) wrath. Things are now so bad, in fact, that Adobe had to warn investors about it in a regulatory filing.

"To the extent new releases of operating systems or other third-party products, platforms or devices, such as the Apple iPhone or iPad, make it more difficult for our products to perform, and our customers are persuaded to use alternative technologies, our business could be harmed," Adobe said Friday in the filing.

Translation? Apple is gunning for us. And it's scary.

This escalating battle had been centered around the Flash video software. Adobe has made a pretty good business developing Flash. The software is used by everyone from YouTube to The New York Times.

In fact, more than 96% of Web users have Flash on their computers, Bloomberg reports.

But Apple is having none of it. In fact, it has made its iPhone and its hot new iPad tablet incompatible with Flash. So if iPad users visit a Web site that has a Flash-based ad or video on it, they can't see it.

Apple's chief executive, Steve Jobs, reportedly has said that Flash hogs memory and has security problems. It's awfully convenient that Apple is introducing a new advertising platform called iAd.

Apple's assault on Adobe went a step further this week. The Daring Fireball Web site notes that Apple has a new iPhone developer license out that appears to squash the use of Adobe's Flash-to-iPhone compiler. That's a workaround coming out soon in Adobe's new software, Creative Suite 5.

"Wonder what Adobe does now?" writes Daring Fireball's John Gruber. "CS5 is thisclose to release and the iPhone compiler is the flagship feature in this version of Flash."

People are still speculating why, exactly, Apple has done this. Writes The New York Times:

It is not clear why Apple would want to cause trouble for Adobe in this way, but one explanation may be that it wants to make it harder for developers to create an application for one platform, like Flash, and then pop out versions for other platforms, like the iPhone or Google’s Android.

At any rate, Apple seems pretty intent on derailing Adobe's plans for Flash, and that's gotta be making Adobe executives -- and investors -- nervous.