A computer virus designed to inoculate against another infection brought down some computer networks Tuesday, forcing Air Canada to check in passengers manually at airports across the country. Long lines formed at counters at Vancouver International Airport as the virus slowed Air Canada's computer system, spokeswoman Laura Cooke said.

The virus, of the self-spreading kind known as a "worm," affected the airline's call center in Toronto and check-in systems across the country, she said. Symantec, an Internet security company, designated the worm a "Level 4" threat -- the second-highest -- due to reports of severe disruptions on corporate networks.

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