It's 11 p.m.; Do you know where your company's checkbook is?

Check tampering is one of the most expensive types of employee fraud, according to forensic accountant Bob Garvey, who writes about how to guard against it in the August-September 2010 issue of ICCFA Magazine.

Garvey says of the most basic things you need to do is make sure checks are well secured. "I have been in offices where the checkbook or blank check stock is left unattended on desks, in the coat closet or on shelves next to the printer, greatly expanding the number of people with access to checks," Garvey says.

This is a potentially very costly mistake, because the chance that your bank will catch a forged or altered check is very small, Garvey says. Furthermore, if your internal controls are deemed inadequate, you could be found "comparatively negligent" and therefore responsible for at least a portion of the loss.

Treat blank checks and check stock as cash; lock them up and severely limit access, Garvey says.

Read more on this topic in the August-September issue of ICCFA Magazine.