I just did some further research on this verse. There are two versions of the LXX because Theodotion's version of Daniel was adopted in place of the Old Greek (LXX) version of Daniel, which was thought to have been poorly translated. The two are contrasted below:
OG LXX: ...heós an apomanósin ho polloi kai plésthé hé gé adikias "until the many rage furiously and the earth will be filled with unrighteousness".
Theodotion: ...heós didakhthósin polloi kai pléthunthé hé gnósis "until many are taught and knowledge is increased".
The MT hd't "knowledge" is commonly thought to be a scribal error for hr'h "evil", as תעדה superficially resembles הערה. Theodotion's rendering reflects the MT and one commentary suggests that didakhthósin, which agrees thematically with gnósis "knowledge", was an error for diakhthósin (sorry, I can't get the gloss on this word). Regarding the OG version, there is a parallel in 1 Maccabees 1:9: "there were evils increased in the earth (epléthunan kaka en té gé)", which itself recalls Genesis 6:5: "the wichedness of man was great on the earth" (epléthunthésan hai kakiai tón anthropón epi tés gés).