(Reuters) — Bankrate Inc., which runs websites comparing personal finance packages, said U.S. regulators were investigating its financial reporting during 2012 and that its chief financial officer of eight years had resigned, effective immediately.

Bankrate's shares fell as much as 23% to a 20-month low after the company said the U.S. Securities and Exchange Commission was examining the improper accounting of more than $1.5 million of accruals and expenses.

The operator of websites such as Bankrate.com and CreditCards.com said its financial statements for fiscal 2011-2013 should not be relied upon, pending the conclusion of an internal review.

The market may be reacting to the risk that Bankrate's statements were fraudulently presented or otherwise misrepresented, SunTrust Robinson Humphrey's analyst Andrew Jeffrey said in a note.

"While anything is possible, we would be surprised if the SEC investigation announced this morning reveals any 'smoking gun' accounting malfeasance," Mr. Jeffrey said.

Bankrate said three accruals of revenue totaling about $781,000 and two adjustments to reduce accrued expenses totaling about $850,000 were being investigated.

The SEC is examining whether accounting entries for the quarters ending March 31 and June 30, 2012, may have improperly affected reported results, the company said.

North Palm Beach, Florida-based Bankrate said it was providing the SEC with documents and information.

Bankrate also said Edward DiMaria, who joined as CFO in 2006, had resigned from that post but would continue as senior vice president.

Mr. DiMaria would be replaced on an interim basis by Steven Barnhart, who was most recently CFO of Sears Hometown and Outlet Stores, the company said.

The company, which went public in June 2011, collects and publishes data on mortgages, car loans, banking fees and retirement savings, among other financials.

Bankrate's shares were trading down 16% at $11.62 in late-morning trading, recovering from a low of $10.66 earlier in the session on Monday.

Up to Friday's close, the stock had lost about 21% of its value this year.