Security Flaw Discovered at Online Bank

X.com Bank, new online bank that is division of First Western National Bank, permitted customers for almost a month to transfer funds from any other account in nation's banking system; as a result, someone armed with another person's account number and bank routing number could move money from that account to Internet bank, then withdraw it; vulnerability was apparently discovered and exploited by at least one Internet grifter; company's executives acknowledge that they contacted law enforcement officials because of one incident, but say dollar amounts involved 'are not significant'; X.com chief executive William Harris says company has changed its procedure for authorizing new accounts after it had discovered about 10 instances in which inaccurate or suspicious numbers had been entered into online application forms (M)