Beating a two session max!

There are various possibilities of detecting multiple instances, some also includes kernel objects. Using network is not really a smart solution and unlikely to be used.

Also have a look here

hxxp://www.codeproject.com/cpp/avoidmultinstance.asp
hxxp://www.flounder.com/nomultiples.htm

By the way, which application is that ?

Visu

As "Visu" said , there're various possibilities of detecting multiple instances . One of these coul be a semaphor declaration . To avoid runing of another instances , you can declar a semaphor with special name and at the bigining just create your named semaphor and if the API return by ALLREADY_EXIST error , it shows that another instance has been run later .