INDIANAPOLIS -- The private information of thousands of Indianapolis Power and Light customers was inadvertently posted online for up to four years, officials said Monday.

The information affects 3,000 residential IPL customers from 2003 until November 2007.

IPL said the data included names, addresses and Social Security numbers that somehow ended up on an accessible server on the Internet.

Most of the information was out in the open for several weeks. Some other files were exposed for as long as four years.

A recent audit caught the error. IPL is sending out letters to affected customers and is offering a year's worth of free credit monitoring and identity theft insurance.

IPL also set up a hot line to deal with inquiries about the situation. The number is 317-261-4845.