All of my users are connected to the Oracle server. One m/c suddenly stopped working and is giving error tns packet writer failure. Basic network connections are working like ping, etc. Could it be a virus?
Sure, anything's possible. If the problem is isolated to a single client and no other users are having the same problem, then it's possible that the failing client has picked up a bug somewhere. It's also possible that they've installed a personal firewall, they've altered their networking configuration (or a recently-installed application has done that without their knowledge), or even that the NIC on the system is starting to fail.
SQL*Net tracing would provide more information, but that may be overkill for now. Your instincts are probably right and getting the latest virus scanner and current patterns to perform a full system scan is probably the first order of business.
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