Rogue current and former dictators and global bribe-paying giant corporations are enjoying levels of impunity, placing them seemingly above the law, which only encourage international corruption and money laundering. The Group of 20 -- the forum of the leaders of the world's most powerful economies -- meets at summit level in November and needs to use this event to forcefully declare 'NO IMPUNITY.'

It is encouraging that the G20 is gradually moving in this direction. In this context, actions were agreed in advance of the meeting of finance ministers of the Group of 20 in Australia on September 19 and 20 to end the tax practices of companies like Apple, Amazon and Starbucks that evaded high rates in countries where they have huge markets by registering their businesses in low business tax countries like Ireland and the Netherlands. These tax approaches have been legal, but they prompted public outrage. The politicians felt the heat and have started to take measures.

But, the G20 needs to go much further. It should build on its anti-tax avoidance initiative to take on the crooks by strengthening the G20's existing 'Anti-Corruption Action Plan.' President Obama and the other world leaders, when they hold their summit on November 15 in Brisbane, Australia, should focus on the grand corruption that involves vast sums being stolen, ultimately, from citizens across the world.

Let us just look at a few of the major cases that need to be addressed, from the plunder by the current ruler of Sudan, to the vast theft by the former president of Ukraine, to the activities of one of the world's biggest banks, as well as possibly vast international bribe-paying by the world's biggest retail corporation. These cases are just the tip of the iceberg of political and corporate corruption that demands G20 action.

Example: BNP Paribas, France's largest bank. In early July it pleaded guilty to U.S. Justice Department charges and paid a $8.9 billion fine (the largest ever for money laundering) for violating U.S. sanctions on Sudan, Cuba and Iran. The Justice Department stated that the bank had taken deposits over many years from these countries into its Geneva office and then changed the identities of the account holders so that they could illegally acquire U.S. dollar investments.

The charges indicated that billions of dollars were laundered for Sudan and that means the accounts of Sudan's dictator Omar al-Bashir and his cronies. Al-Bashir is wanted by the International Criminal Court for massive human rights crimes directly related to the slaughter of thousands of people in Dafur.

Several years ago, Wikileaks, according to The Guardian newspaper, revealed that the Sudanese leader had 'siphoned as much as $9 billion out of his impoverished country, and much of it may be stashed in London banks.'

There is no evidence that U.K. authorities have investigated these allegations. There is no evidence that BNP Paribas is no longer serving as Sudan's banker or that the French authorities care. No top banker at BNP, or, for that matter, any of the major banks caught by the U.S. Justice Department for money laundering and sanctions violations, have been hauled into court and prosecuted.

Example: former Ukraine president Viktor Yanukovych. Ukrainians where aghast when Yanukovych was forced out of office in February to see the incredible riches of his gold-plated mansion in Kiev. Politicians claimed he had stolen at least $20 billion and perhaps double or triple that sum. Immediately, Swiss and Austrian authorities announced they were blocking bank accounts in their countries belonging to the dictator. In June, the Ukraine authorities announced they were investigating the links of two domestic banks to the former leader.

However, the Austrian and Swiss authorities have not revealed which banks held the stolen cash or how large the assets are that are frozen and whether they will be returning the money to the people of Ukraine. Meanwhile, the dictator or his cronies who have the foreign assets, which were almost certainly laundered through holding companies in countries like Cyprus, Liechtenstein and the Cayman Islands to hide the real owners of the accounts, have been pressured to reveal where the stolen money is.

The vast funds stolen by corrupt leaders, like Yanukovych, or the former dictators of Egypt (President Mubarek) and Tunisia (President Ben-Ami) have not been seized by Western authorities and returned to their rightful owners -- the citizens of their countries. The G20 needs to act to close the money laundering havens and ensure asset repatriation.

Example: Walmart, the world's largest retailer. In March, the company announced that over the previous two years it had spent $439 million conducting internal investigations of bribing foreign government officials in Mexico, China, India and Brazil. It was not the U.S. Justice Department that prompted Walmart to become alarmed. It was an investigation the New York Times in 2012.

There are many other cases of international corruption where the justice departments of G20 governments have either turned a blind eye or done very little. Challenging this complacency is a brand new global campaign launched by the anti-corruption organization, Transparency International, which is called: 'Unmask the Corrupt.' It seeks to expose the corrupt villains -- individuals and corporations -- as well as the schemes they use to launder their cash and, as a result, buy yachts harbored in the South of France, mansions in London, Manhattan and Beverly Hills and the world's most valuable works of art.

It is now time for the G20 to do some unmasking. It needs to use its summit meeting and put an end to the impunity that is so widespread.