Is an attorney prohibited to do either of two things after severing his relationship with a former client?

" '[A]n attorney is forbidden to do either of two things after severing his relationship with a former client. He may not do anything which will injuriously affect his former client in any [matter] in which he formerly represented him nor may he at any time use against his former client knowledge or information acquired by virtue of the previous relationship.' " (People ex rel. Deukmejian v. Brown, supra, 29 Cal.3d at p. 155, 172 Cal.Rptr. 478, 624 P.2d 1206.)