z2net.dll is a file that belongs to the z2net.dll Module program. If this file gets corrupted or goes missing, you may have an error problem in your registry. You may have initially thought that you acquired a virus, but the likelihood is that you simply have a file that is corrupted in some way. You need to have it cleared by a registry cleaner.
ZookaWare PC Cleaner is a registry cleaner that offers a free initial scan to look over what may be troubling your computer. It will give you information about this file and will give you information about other files on your computer that may be a problem, as well. It is up to you to then invest further into ZookaWare PC Cleaner. You can set ZookaWare PC Cleaner to scan regularly to make sure your registries are running clean as a whistle.