After Heidi Pratt's jaunt to the courthouse last week to file for separation from Spencer, a lot of people speculated that she did it to protect her financial assets. (Word on the street is that Spencer's strapped for cash, so according to gossip, his estranged wife wanted to ensure that he couldn't spend her money.)

Of course, many of you don't even believe their split is actually real.

According to RadarOnline.com, Heidi has upped the ante and hired a private investigator to track her ex-hubby around town. "The Hills" star is said to be worried that Spence has been spending THEIR money on another woman (oh, hell no!).

"Heidi has hired a former member of the sheriff department, who now works as a private investigator, to look into it," the site's source said. "It is really important to Heidi to find out if Spencer has been cheating on her."

Hmm. Is it cheating if you're broken up, or only if you're pretending to be? More to be revealed soon...