Microsoft gets flak when there are macro virus alerts. Each iteration of Microsoft Office has toughened up default security. Excel 2007 now displays a security alert when you open a workbook which has external workbook references. MSKB 826921 explains the issue and workaround.
No need to work so hard. There is a deep menu nested way of switching off the alert – thanks to Lilith for telling us.
Office Button > Excel Options > Trust Center > Trust Center Settings > External Content > Enable automatic update for all Workbook Links (not recommended).
Yeah, not recommended but do it anyway – of course you should have a good, up to date, anti-virus system in place and running real time.
Don’t confuse this with:
Data > (Connections Block) Edit Links > Startup Prompt > Don’t display the alert and update links