Qualifying for the Mortgage Interest Deduction. Mortgage interest includes that which you pay on loans to buy a home, on home equity lines of credit and on construction loans. The deduction is limited to interest paid on your main home and/or a second home. Interest paid on a third or fourth homes isn't deductible.
The statute of limitations on how far back the IRS can audit (called the Assessment Statute Expiration Date or ASED) varies depending upon the circumstances of the tax return. In most cases the IRS will not go back more than 3 years unless there is something very wrong with the tax return that was filed.
The IRS is going after offshore income and assets in a big way, and that dovetails with another IRS audit rule. The IRS also gets six years to audit if you omitted more than $5,000 of foreign income (say, interest on an overseas account). That matches the audit period for FBARs, offshore bank account reports that can carry civil and even criminal penalties far worse than those for tax evasion.