The problem of interconnected computers is the problem of corrupt data. If a noncompliant machine sends noncompliant data into a compliant machine, the former destroys the integrity of the latter's data. This is why y2k is a systemic problem. To guard against corrupt data, the compliant computer must be permanently segregated from the noncompliant computer. This destroys every large system. The classic example is banking.
The IRS cannot escape this problem. It has too many external trading partners.
This is from the IRS Web site on y2k.
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An External Trading Partner is anyone outside the IRS with whom the IRS exchanges data, either magnetically or electronically, as the source of the data or as the recipient. This includes a wide variety of exchanges, such as the various extracts provided to state tax agencies, data provided to agencies under reimbursable agreements, and those who file electronic returns and magnetic filers of information returns.