By Lucy Williamson
Former BBC Jakarta correspondent
Jakarta's Marriott hotel has been attacked twice in the past six years
It took just a few minutes on Friday morning for Indonesia to be jolted back to the early years of this century - to a time when annual bomb attacks by militant Islamists linked to the group Jemaah Islamiah terrorised the country.
Friday's bombs seem to bear all the hallmarks of those earlier attacks.
The targets were luxury hotels used by foreigners in the most developed part of the capital, Jakarta. One of the hotels, the Marriott, has even been hit before.
The method too appears to be familiar. Initial reports said the bodies of two suicide bombers had been found at one of the sites.
It feels all too much like the bad old days - the days of 2002 when attacks on the tourist island of Bali killed more than 200 people; or of 2003 when the Marriott suffered its first attack; or 2004 when the Australian embassy was hit; or a year later - again in Bali - when suicide bombers blew themselves up in beachside restaurants.
Jemaah Islamiah (JI), or the radical networks it spawned, have been blamed for every one of those attacks.
And all eyes will once again be on them.
But the militant landscape in Indonesia has changed since those years of violence.
The attack of 2002 actually split opinion within the militant group - with those who supported this kind of attack on civilian targets splintering off to form smaller, more radical units.
One of the most high-profile of these is run by a man called Noordin Mohammed Top - still at large despite a long-running police campaign to catch him.
Dec 2000 - Church bombings kill 19
Oct 2002 - Bali attacks kill 202, many Australian
Dec 2002 - Sulawesi McDonalds blast kills three
Aug 2003 - Jakarta Marriott Hotel bomb kills 12
Sept 2004 - Bomb outside Australian embassy in Jakarta
Sept 2005: Suicide attacks in Bali leave 23 dead, including bombers
He and others like him are still actively recruiting, say analysts.
And the repeated exposure by police of radical cells working in the country show that the movement has not been stamped out entirely.
But it has been weakened.
Supported by Australia, the US, UK and others, the Indonesian police have made hundreds of arrests over the past few years, and killed or captured many of the most senior suspects.
This has led to a serious lack of experience and technical expertise within the networks.
That may have been filled by expertise from abroad - perhaps from the southern Philippines where a long-term conflict is being waged between Islamist groups and national security forces.
Another factor cited by the Australian security think-tank ASPI is the recent release of JI prisoners from Indonesian jails, which may have reinvigorated radical groups.
That is not something everyone agrees with. But in the end, this attack may have been simply waiting to happen.
For all the police's success, the determination of groups like Noordin's to carry out attacks has remained strong.
And the operations themselves have become smaller and more mobile.
In 2005, the bombers switched from using car bombs to strapping the explosives on their bodies - a tactic that may have been used again here, right in the centre of Indonesia's economic and political heart.
It is a chilling message - and one that will resound loud and clear across the country.
Lucy Williamson was the BBC's correspondent in Jakarta from June 2006 to June 2009.