If you have a paid membership, you can remove names from your own profile visits. Simply click Remove next to the name you wish to remove. At this time, there's no option to remove names in bulk or to block members from leaving a profile visit.
If you'd like to remove a profile visit you left on another member's profile, just return to that profile and click Remove visit. Profile visits can be removed within one hour after you first visit.
If a profile visit was removed automatically, it may be that the member removed it themselves, or deleted their profile. People may choose to remove themselves from Classmates® at any time, in which case they will no longer appear in your profile visits.