IAG has warned shareholders to beware of undervalued offers for company shares, with estimates showing company investors have lost around $17 million on lowball offers since 2002.

The insurer – which has the largest number of retail investors of any major listed company – says a company trading as Hassle Free Shares has been contacting its shareholders with offers significantly below the current value.

A second company, Direct Share Purchasing, has also requested information from the IAG share register that the insurer believes may be used to launch another offer for IAG shares.

IAG says Direct Share Purchasing is associated with notorious share trader David Tweed, whose companies have previously made undervalued offers to its investors.

The insurer is obliged under the Corporations Act to provide register information.

Almost 16,000 IAG shareholders have accepted undervalued offers from share buyers since 2002, with an estimated cumulative value transfer of about $17 million.