Windows 9x used a TTL of 32. I vaguely recall hearing that it caused problems in extremely exotic cases, but that could have been misinformation. I imagine that >99.999% of the time, 32 is enough. This makes fingerprinting via TTL to distinguish between those who set it at 32, 64, 128 and 255 (OpenSolaris and derivatives) viable. That said, almost nobody uses Windows 9x or OpenSolaris derivatives on the internet these days, so I used values from systems that they do use for my argument that fingerprinting via TTL is possible.