A structured investment vehicle (SIV) was a type of fund in the shadow banking system. Invented by Citigroup in 1988, SIV's were popular until the market crash of 2008. The strategy of these funds was to borrow money by issuing short-term securities at low interest and then lend that money by buying long-term securities at higher interest, making a profit for investors from the difference. SIVs were a type of structured credit product; they were often from $1bn to $30bn in size and invested in a range of asset-backed securities, as well as some financial corporate bonds. SIVs had an open-ended (or evergreen) structure; they planned to stay in business indefinitely by buying new assets as the old ones matured, with the SIV manager allowed to exchange investments without providing investors transparency or the ability to look through the structure. As of October 2008, no SIVs remained going concerns.