Account numbers are public information, and should be treated as such. MIT's financial system is based on openness, and the assumption that account owners will check for unauthorized or erroneous transactions and can get them reversed.
As a group officer, this means that you should not need to be concerned about revealing your account number, and should regularly check for incorrect transactions. On the part of vendors, this implies that knowing an account number should not be treated as evidence of authority to spend against said account. Vendors can use our Account Lookup page to see what group an account corresponds to, and who can spend against it.
Account numbers are available through several different sources. If an MIT affiliate seriously intended to steal money from an account, then they could undoubtedly find the account number.
RolesWeb is the primary tool intended for MIT affiliates to look up information about accounts and account numbers. This website makes available all account numbers at MIT, along with who has what authorizations on then (spending money, reporting on them, etc.). For example, most student group accounts are listed on one page. A Google search for "find cost object site:mit.edu" finds RolesWeb on the first page of results.
The new ASA Database introduced around Fall 2011 also includes account numbers. We made this decision partially to create an expectation that account numbers are public and to decrease the number of vendors and club officers that have an expectation that this information is treated as secret.
If you have specific vendors that appear to be considering these numbers confidential, or have other specific concerns about fraudulent use of account number information, please contact us so that we can work on eliminating those avenues of abuse.