What's the difference between a microfilter and a purifier?

Microfilters (most pump filters in this list) remove bacteria and protozoa like Giardia and Cryptosporidium but generally not viruses. Purifiers — like the Survivor Filter PRO with its 0.01-micron stage — also handle viruses, which matters more for international travel or heavily contaminated sources than for typical North American backcountry water.