I personally don't believe in this possibility on any a short to long term future.

It took years and dozen of millions of dollars to top class team of microbiologist (Eckard Wimmer) to synthesize the Polio in 2002 and this virus is relatively simple (7000 base). The Smallpox is much bigger (180 000 base) and would be complex to synthesize. More recent work have managed to assemble the entire genome of a bacterium (580 000 base pairs) but in the case of bacteria, synthesizing the DNA is not sufficient to create a synthetic life form (for example, you'd need to synthesize the rest of the component of the cell and somehow jump start the metabolic processes). If one has enough money to start this task, why wouldn't he try to take a known virus or bacteria and change its DNA to make it more potent or resistant to treatment ? Would be a better strategy. Also, since 2001, the US government stockpiles enough vaccine to protect the entire population (this is theoretical as vaccine are effective before contamination and a newly created smallpox may or may not respond well to the vaccine). That being said, the rapid advance of synthetic biology is a concern but creating a bio agent is very time and resource consuming and it's only a small step of the equation. You need to weaponize it and spread it effectively. I meet many expert and the opinions are very polarized on this questions, some says it will be a threats while others are not very worried.

Also, "cooking" a new bio weapons is only one part of the equation. You must have very strict containment and safety measures in the lab and be able to spread the agent in real life.

As former soviet chemical weapon program specialist Vil Mirzayanov said in one of his report, the terrorists would kill themselves long before they hurt anybody if trying to play with nasty stuff. Actually one of the Aum member almost killed himself during an attempt of Sarin release. Their truck got on fire during the process and he was exposed to Sarin. Luckily they had medical team and atropine. This might explain why they finally released Sarin in a crude manner, using plastic bags to disseminate the agent on the subway floor.