Store.exe on Exchange Server is running

Unless you have a very underpowered server you have some kind of problem. Many things could cause the 100% usage. Go through MS's checklist:

http://support.microsoft.com/support/kb/articles/q172/8/13.asp

Good luck!
-Heath

The first answer is right on but to add to that, the same symptoms appeared on our server when the drive that was holding the store.exe started running out of disk space.

Good luck and hope this helps.

This may be normal behavior for NT Server. If you are not experiencing performance problems, I would not be concerned. Check the following Microsoft Knowledge Base article:

Q157044.

However, if you find that performance is lagging, there may indeed be a real problem. Check the following articles. If you do have a problem, they may help you to pinpoint it and provide a solution.

Q181410
Q243581
Q197491