For years, Microsoft has offered some of its most generous software deals to its partners and software developers.

The subscription-based MSDN and TechNet offerings allow consultants, resellers, and software developers to roll up their sleeves and try out just about any Microsoft program, past or present, for a low annual subscription rate. For an annual subscription price of $349, TechNet Professional subscribers get access to nearly every release of every operating system (desktop and server) and Office suite that Microsoft has ever made. MSDN subscribers pay more but also get access to a cornucopia of software.

It’s a tremendous deal. Maybe too good a deal, in fact, as software pirates long ago discovered that the product keys delivered to MSDN and TechNet subscribers could easily be resold along with counterfeit discs.

The result was practically a license to print money. Last month, at a client’s office, I inspected 10 copies of Windows 7 Professional that my client had purchased from a web-based retailer for more than $100 each. The software was counterfeit, but it looked good enough to pass a cursory inspection. And the keys were taken directly from a $349 TechNet subscription.

That’s $1000 in revenue on that one transaction alone, and the pirate behind the operation still had hundreds of keys to resell—for other versions of Windows, for multiple versions of Office and individual Office programs, and for Microsoft server software.

In all, that pirate could easily collect tens of thousands of dollars in revenue by illegally reselling license keys from a single low-cost subscription.

So, if you’re Microsoft, how do you fight back against that kind of determined piracy?

You tighten the terms on those subscriptions, of course. And in the process, you inspire howls of protest from current subscribers.

Microsoft cut TechNet product key allotments back in March, for the second time in two years. Now it’s making additional changes to the TechNet and MSDN programs, with the goal of making them less attractive to pirates while still keeping them useful for partners.

Here’s what the new subscription terms will entail when they take effect later this month:

Fewer license keys. For current versions of Windows client software and Microsoft Office, the number of product keys that MSDN subscribers will be allowed is reduced from 10 to 5. For older versions, only three keys are allowed. TechNet subscribers will continue to be allowed three product keys per version.

Fewer keys available per day. If you’re an MSDN or TechNet subscriber, the number of keys you can claim per day will be reduced from approximately 55 to 10. The intent, of course, is to prevent would-be pirates from paying for a new subscription and then quickly claiming hundreds of product keys and reselling them to unsuspecting customers.

Fewer products. In current editions of these subscription-based offerings, you can download any version of Microsoft Office as well as the standalone products that make up the Office collection. When the new terms kick in, all of those standalone programs will be removed, along with older, unsupported software versions. You’ll no longer be able to download Office 97 or Windows 98, for example.

For TechNet customers, the biggest change of all is the elimination of perpetual license rights. Currently, you’re allowed to continue using any software and product keys you download as part of your TechNet membership, even after your subscription expires. Under the revised terms, new and renewing subscribers will get time-based rights that apply during the subscription term only. The new, simplified subscription agreement makes it clear:

The subscription provides you with access to software and associated benefits. When your subscription concludes, you will no longer have access to the software or any associated benefits and must discontinue your use of the software.

That doesn’t mean that the software itself will stop working, of course. Instead, the license expires along with the subscription, and you’re expected to stop using the evaluation copies.

Although the changes sound drastic, the actual impact should be minor for most subscribers. Each product key can be activated multiple times, which means that an allotment of 3-5 keys can used for dozens of installations. A legitimate subscriber can also request additional keys, and Microsoft says that each such request should be honored within three days. The company says it has also beefed up its support escalation process to deal with potential issues caused by the change in terms.

The new TechNet subscription agreement (four pages of plain language, compared to the current 15 pages of legalese) also makes it clear that the program is for evaluation and isn’t intended as a way to acquire cheap licenses. These bullet points are in section 4 of the new terms:

You may not use the software if you do not have an active subscription.

You may install and use the software on your devices only to evaluate the software.

You may not use the software in a live operating environment, in a staging environment, or with data that has not been backed up.

If you’re a current subscriber to any of the affected programs, you have a couple weeks before the new terms take effect. Product keys you claim now will remain available later, as will software you download.

Given the scope of piracy, these changes are understandable, but for longtime subscribers they’ll be a bit of a shock. Cue the howls of protest in 3, 2, 1 …