MathType 6.8 was a "polish" update. By this time, Microsoft Office 2013 had changed the rules. Older versions of MathType often crashed or inserted garbled equations into the new docx format. Version 6.8 was the hero that fixed this.
Design Science tried to patch it with 6.8b, but the damage was done. To this day, if you find an old "MathType 6.8 full crack," it is almost certainly that university's legitimate key floating around. mathtype 6.8
Here is the specific story associated with 6.8: MathType 6
Before MathType became a subscription service owned by WIRIS (and later, min Reform), it was developed by a company called Design Science , based in Long Beach, California. They created MathType as the professional version of Microsoft Equation Editor. For over a decade, version 6.x was their flagship product. Version 6
Because MathType was expensive (~$97 for a student license in 2013), many students used keygens. For versions 6.7 and earlier, those keygens worked fine.
However, a major European university purchased a site license. A student inadvertently leaked a Volume License Key (VLK) for 6.8 to a popular cracking forum. Because 6.8 didn't "phone home" for every launch (it just checked the key format), that single VLK worked for millions of users worldwide for nearly 5 years.