This excerpt taken from the VIRL 8-K filed Sep 9, 2008.
Accounts receivable consists of amounts billed currently due from customers. The allowance for doubtful accounts is the Businesss best estimate of the amount of probable credit losses in the Businesss existing accounts receivable. The Businesss allowance is determined based on historical write-off experience and on specific customer accounts believed to be a collection risk. Account balances are written off against the allowance after all means of collection have been exhausted and the potential for recovery is considered remote.