Well first I'm going to explain what the WinMX Hotlist is not on WinMX network, but this does not apply on opennap. Users in hotlist are not permanent. Hotlist does not accurately reflect online status on its own. If you want to know, right-click the user in hotlist, choose Whois. If it says something like (No response from remote host.) the user has either went offline, or changed remote hosts. Either way your hotlist will not help you at this time.
When a user logs on the WPN (WinMX Peer Network), the default username they chose in networks is adjusted to provide for issues that must be considered in a decentralized network such as WinMX.
The user (CatVomit), automatically has 3 digits added (Network Window). There are an additional 5 unique digits added after the _ . This provides each user with a unique UserID without having the user ID registered at a server. On your hotlist the username +8 digits are what is seen on a hotlist. When a user disconnects from network, or as secondary user changes primary hosts, it causes this ID to change. If it does, then there Is no way to use this hotlist entry to access the user desired.
Even more importantly is the next set of numbers. 9f2af5181871 . This is the ip and port the user is connecting with/though. If primary it's their ip:port, if secondary, it's the ip of the primary they are connected through.
One solution is to search for a file you know the user has shared. This is often unsuccessful because WinMX is decentralized and searches are not all encompassing. Searches tend to show different results because the network is in a state of constant flux.
Another solution is more likely to find the person you are looking for, but it requires an effort by both parties. It is to agree to meet in a WinMX chatroom , there you can browse, personal message etc each other from there.
In short term reboot situations, there is a workaround that has a good success rate. Add the user(s) that you wish to continue contact with to your ignore list. Close WinMX, ........ when you reopen WinMX, open your ignore list, from there you can add them to hostlist or pm them. If they haven't disconnected from network since you last had contact, the username in hotlist will still be valid. A little work, and preparation, but it can work.