The drop in a key interest rate to a 66-year low is a sign of one thing — fear.

Traders don't actually think a Treasury note paying 1.62 percent is a good investment. They just trust Uncle Sam to keep their money safe if Europe falls apart.

"When people just want to get their money back, there's not a lot of competition," said Bill O'Donnell, head of U.S. Treasury strategy at the Royal Bank of Scotland.

The benchmark 10-year Treasury note fell Wednesday to its lowest level since November 1945 as worries about the European debt crisis roiled markets worldwide. Investors sold off stocks and plowed money into government bonds that are considered safe.

The search for hiding places was spurred by news out of Spain, the latest trouble spot in the region's debt crisis. The European Central Bank said Spaniards pulled billions in deposits out of their banks last month, raising concerns of a larger bank run.