What is causing calls to sharepoint server vti_bin\sites.asmx

We are looking at logs on our sharepoint and see a call to this web service from 开发者_运维技巧several PC's.

The calls apprear very regular every 5 mins, when the PC is on.

Anyone know what is causing this?

Edit

The agent in the iis log is: Mozilla/4.0+(compatible;+MSIE+6.0;+Windows+NT+5.1;+HO32602;+HO32600;+HO32501;+.NET+CLR+1.1.4322;+.NET+CLR+2.0.50727)

In addition to the above (which is likely) it could be one of the desktop search products that MS has created.

Maybe:

• Office

• Workspace/Groove sync

• Some custom client application

• SharePoint Designer

• Browser

Whats the user agent reported in the logs?