Corporations cannot donate money to campaigns at all, either directly or through PACs. A corporation can have a "captive" PAC whose expenses it can pay (for example, letting it operate out of their corporate offices), but all donations that pass through to a campaigh must come from individuals.
When you hear that "Company X gave money to candidates", what you're really hearing is "people who reported that they work for Company X gave money to candidates."
OpenSecrets has been sweeping that disclaimer more and more under the rug, to the point where now I'd accuse them of lying.