I'd use a hash for this rather than an array, something along these lines:

%supported_security = (
    "WPA"    => "WPA",
    "WPA2"   => "WPA2",
    "WEP 64" => "WEP 64",
    ...
);
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And then just probe that hash in order of preference of security type:

$best_type = $supported_security{"WPA2"}
    // $supported_security{"WPA"}
    // $supported_security{"WEP 128"}
    // ...
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with // being the logical defined-or operator (see Logical Defined Or); if that's not available on the version of Perl you're using, use || instead.