[quote name='dallow']How would you even know someone hacks an account?[/QUOTE]
They have outrageous gains that make absolutely zero sense.
For example, Dead or Alive Xtreme 2. In order to unlock one achievement, you have to purchase all a girl's swimwear for that girl. Based on my math (and this is using the casino exploit that was patched), it'd take about 3 hours for just one. I think there's maybe 7 girls. That's at least 21 hours for 140 points. The other remaining achievements consist of buying every piece of swimwear in the game for every single girl. There's just no way humanly possible for someone to earn all those in a 24 hour period. And to my knowledge, there's maybe a handful of guys in the world that have done it legitimately.
Other odd flags are 1000/1000 in Rumble Roses in a 24 hour period. Time achievements that unlocked back to back (For example, Viva Pinata's 10 hour then 50 hour achievements). Older games that require you to beat every single difficult done in a 24 hour period (games that require more than say 6 hours to complete a single play through for example)