ST6 Maintenance Packs can be downloaded from: https://download.industrysoftware.automation.siemens.com/solid_edge/ST6/
If you're using Norton Internet Security, you'll get an a screen like this:
Just click "Run this program anyway"
You also may get this when starting Solid Edge next time....
Again just click on "This program installed correctly"
Everything works fine... you should not have any problems.