You will learn that the area surrounding water filter selection is confusing and is clouded with deceiving marketing claims. That is why it is important to use a scientific approach in making these choices and the CDC does a great job.
The CDC reports that there are two types of these filters , "absolute 1 micron" filters and "nominal 1 micron" filters. In light of this you will learn that not all filters that are supposed to remove objects 1 micron or larger from water are the same. The absolute 1 micron filter will more consistently remove Cryptosporidium than a nominal filter. Some nominal 1 micron filters will allow 20% to 30% of 1 micron particles (like Cryptosporidium) to pass through.
According to the CDC, "...filters that have been tested and certified should have wording on their labels indicating that they have been listed and labeled to NSF/ANSI Standard 53 or Standard 58 for cyst removal or cyst reduction by an ANSI-accredited certification organization. To find out if a particular filter is certified to remove Cryptosporidium, you can look for "NSF 53" or "NSF 58" plus the words "cyst reduction" or "cyst removal" on the product label information. If you chose to use a non-certified product, select those technologies more likely to reduce Cryptosporidium, including filters with reverse osmosis and those that have an absolute pore size of 1 micron or smaller." Further details are available in the CDC publications, A Guide to Water Filters and Drinking Water Treatment Methods for Backcountry and Travel Use
You need to be very cautious about accepting any type of backpacking filter that claims to remove viruses. I have not been able to find any conclusive testings that were controlled studies of actually removing a virus. There are studies that show no viruses present but provide no data as to whether any viruses were present to begin with or of what pathology.
Consider never limiting your water disinfecting to filtering only but always use a chemical as prescribed to completely disinfect drinking water where boiling is not possible.
Since 2002, Steve has been warning our nation that it will again enter into another Great Civil War and that it will be one of Lawlessness vs Civil Order.