Marcel Thee – Bombers are decorating Jakarta. Not with explosives, but with cans of spray paint. And lots of it.

"Bombers" refers to the increasing number of graffiti artists prowling the streets of the capital.

Better known as mural or graffiti artists, these bombers often operate outside the law due to the restrictions against their art form, which is often seen as "polluting" the city.

They attempt to get around the law by working the midnight shift, waiting until the streets are empty before they bring out the spray cans. But even then they must still engage in a game of hide-and-seek with police and public order officers.

Chances are you've seen some of their work on the city's underpasses, tunnels and public walls. Not the erratic scrawls and scratches of swear words, but the graffiti pieces that look like they were carefully designed, complete with contrasting colors and detailed graphics.

Graffiti art itself is nothing new in Indonesia. It has been here since the early 1990s. It's only in the last few years, however, that the quality has improved and the bomber community has strengthened.

Twenty-five-year-old Eko Pratomo, who calls himself Silentboy, a bomber who works as a graphic designer and illustrator by day, says, "I would say that graffiti art has been here since around 1994 and experienced a boost in quality and popularity by the 2000s."

The emergence of the Internet in the country played a part in popularizing this underground world, particularly for artists looking for new ways to express themselves.

M Ikhwan Hakiki, 22, another bomber, says local graffiti culture "might have already been here since the 1980s."

Local graffiti artists focus mostly on two distinct styles: lettering, which uses spray paint, and mural illustrations, which use regular wall paint.

Ikhwan has been bombing since 2006, when he joined the art community Kampung Segart, from IISIP University in South Jakarta, which had members who were active graffiti artists.

Eko says graffiti is an extension of his love of illustrating. He became taken with it after discovering the New York City-based street art Web site Wooster Collective. By early 2000, Eko himself was actively illustrating the city's walls.

"It's people's reaction of love and hate toward my work that drives me," Eko says. "Some people look at a mural or graffiti and they completely love it, some completely hate it. The public's reaction is fascinating."

Another bomber, Andri Ruay, 25, says the reason he engages in the art is "the freedom of using unlimited mediums and medias; creating absolutely any illustration and publicizing the art straight into the city."

Andri says he and other bombers can be motivated by feeling they have artistic talent that they are stopped from sharing with the public. "These kinds of feelings eventually drive bombers to 'naughty' ideas, and so they directly publish [their work] using public spaces."

By the mid-2000s, there were numerous bombers and "crews" (groups of bombers) operating in Indonesia. Their developing technique and style meant that even international graffiti artists and publications began to take notice. There were also internationally sponsored events.

"Tons of Indonesian graffiti has been featured in books about street art," Eko says. "And [well-known graffiti] artists such as ERY1, from Japan, Ewok and Futura, from the US, L'Atlas, from France, and Killer Gerbil, from Singapore, have paid visits and done work here."

Even representatives from Sneaker Pimps, which bills itself as "the world's largest touring sneakers and street-based art show," have sponsored street art events in Indonesia.

Ikhwan also points to the growing number of shops selling bombing equipment such as spray paint, mural paint and gas masks, as evidence of the burgeoning movement.

Dhani R Manto, 19, who heads a North Jakarta bomber crew, got into bombing by way of hip-hop music and street culture. He says it takes special skills to create graffiti art.

"An artist might be able to draw on computer, paper, canvas or a number of other mediums. But that does not mean he'll be able to create graffiti art. The use of the spray can is particular and you have to get used to it," he says.

Dhani also mentions that a can of spray paint costs around Rp 18,000 ($2), and that each large piece of graffiti costs a minimum of Rp 200,000 to create due to the amount of paint and variety of colors used.

Still, the increasing quality and popularity does not necessarily translate into a greater appreciation for the artists and their art. They still play cat-and-mouse with officials. Eko was arrested during one midnight bombing raid, while Ikhwan has learned to avoid areas with a strong police presence.

"You just have to know good areas to draw," Ikhwan says, pointing to areas in Depok, where he lives, that he believes are safe from the reach of the law.

Eko says there are a few so-called "legal" areas in the city where bombers are allowed to do their work. What he means by "legal," however, are "areas we keep going back to, even after being warned by the police numerous times – they eventually just throw their hands up in the air and let us do whatever we want in those places."

He adds that explaining to officers that their work is art and not just scribbles sometimes helps to avoid trouble.

Eko is proud of the achievements of local bombers. "If you're talking about quality, Indonesian bombers are on par with international artists. In Asia, I would say that we are as good as Japanese artists."

He adds that a few Indonesian graffiti artists have exhibited their works internationally. Andri says he hopes Indonesian bombers will eventually be recognized as full-fledged artists in their own country.

Ikhwan believes recognition of their art would be helped by stronger ties between graffiti artists across the country. "There is still some separation between bombers in different regions. I hope that all of us become increasingly solid," he says