They say you can't keep a good man down. Likewise, it's sometimes hard to keep a bad man down -- if he has a penchant for credit card fraud.

Being incarcerated can make it a little harder to keep business going as usual. But for some people, like the jailhouse entrepreneurs highlighted here, being locked up just means you have a bigger office.

Viagra Empire
Martin Simon Hickman went to jail for illegally selling Viagra online, only he didn't see prison as the impediment to his business that some of us might. After all, why should a little thing like being locked up get in the way of profit and unlawful boners?

After being jailed, Hickman continued to run his Viagra empire from behind bars. The Manchester Evening News over in the U.K. did a bit of investigative reporting and ordered some pills from his Web site. They received some Lovegra pills in the mail a few days later, a probably legitimate but unlicensed version of Viagra. No word on exactly what they may have done to stop him since he was already in prison, though we like to think maybe he was restricted to only checking out 4chan.

Autograph Business
Charles Manson, notorious leader of the Manson Family and all-around mass-murdering maniac, has been running a lucrative autograph business from prison. And -- though it's hard to say if this makes it better or worse -- it's a scam; he hires other inmates to sign his name on things.

Apparently Manson is becoming one of the wealthiest men behind bars thanks to this empire of fraudulent autographs and assorted other mementos that fetch big money.

Prison officials say prisoners are not allowed to run such businesses and have confiscated items from Manson in the past. And though prisoners are only allowed to receive small amounts of money from the outside world, there's no stopping others outside (like Manson's female groupies) from collecting money on their behalf.

Manson has also tried smuggling out clothing and apparently makes tiny scorpions out of socks. No word on what the street value of a Charles Manson sock scorpion is, but it must be worth the effort.

Record an Album
What to do if you're an aspiring rapper who sorta, kinda goes to prison for shooting and wounding three people? Keep living life as normal, apparently.

Jamal Barrow, also known as Shyne, recorded most of his debut album before being sentenced and, once inside, it turned out to be pretty popular.

Shyne got a $3 million deal while in prison and managed to record part of his album, too. Prison officials had to revoke his phone privileges when it turned out he'd made more than 100 calls and even recorded some of his raps over the phone. While violating basically every prison rule about phone use, he even gave interviews from within the prison.

Running the Entire Prison
While many prison businesses involve shady drug deals or guys selling toilet wine for a pack of Lucky Strikes, in Guatemala the prisoners were a little more industrious. For 10 years, an entire prison was run by the inmates themselves while corrupt guards pretended to go to work and just wandered around the outside of the grounds.

Over the course of the decade, prisoners had built restaurants, shops, bars and churches (Catholic and Evangelical) as well as some cocaine labs. The entire thing was run by an organization called the Order and Discipline Committee, the leader of which was pulling in about $25,000 a month.

More successful inmates built homes on or around the grounds, two-story chalets with high-speed Internet connections and flat-screen TVs. Eventually, the government sent in some armed forces to put an end to the prison's shenanigans, presumably rounding up the 1,600 inmates and sending them to someplace really awful, like Branson, Mo.