UPDATE: The IRS has extended the tax-filing deadline for all filers to midnight Wednesday, April 18, due to a glitch with agency's website.

The IRS Direct Pay system is not functioning on the last day of timely tax filing. And it appears that the e-filing system is also at least partially down.

Today is the deadline for most Americans to report their income taxes for the last calendar year and, if taxes are owed, to pay that debt.

It is unclear at this time whether the IRS internet outage is the result of a high volume of legitimate users, or is due to a coordinated external attack. The Washington Post is reporting that the IRS is planning to attempt a "hard reboot" of its system, hoping to get it up and running again.

The IRS is advising everyone to continue e-filing as planned, adding that taxpayers would not be penalized for the technical issues.