Subways and other modes of public transportation near financial institutions could be targets for terrorists, according to a law enforcement bulletin issued by the FBI (search) and Department of Homeland Security (search).

The bulletin, issued on Sunday, also discusses the potential use of airplanes as weapons and about a possible terror plot to conduct computer attacks, according to a copy of the document obtained by FOX News. The bulletin also explains that the terror threat level was raised to orange, or "high," for the financial services sector in New York City, Northern New Jersey and Washington, D.C.

"Recent and credible specific intelligence reporting indicates terrorist operatives have done extensive research and reconnaissance activity against major U.S. and international financial institutions in Washington D.C., Northern New Jersey and New York City," the bulletin states.

The bulletin specifically mentions the buildings that are already known targets — the International Monetary Fund (search), World Bank (search) buildings Citigroup (search) buildings, New York Stock Exchange (search) and the Prudential (search) building in Newark, N.J.

The FBI and DHS also state that there are other possible modes of attack using improvised explosive devices "in subways and other public transport systems in close proximity to these targets. Terrorist use of aircraft as weapons against homeland targets is another mode of attack to consider."

The bulletin also says: "We have limited information indicating terrorist intent and plans to conduct computer network attacks against U.S. financial institutions."

As for the buildings mentioned above, the FBI and DHS say that the intelligence they have gathered does not specify the timing or mode of attacks, although they believe the most likely form of attack to be a vehicle-borne improvised attack. They say that that could include limousines, large vans, trucks and oil tankers, which could be placed in underground parking areas or highly populated entrances.

"The reporting provides a level of detail that is unusually specific, to include information about the interior configurations of these buildings, as well as infrastructure, services and buildings that surround the targets of interest," the bulletin states.

The bulletin also reminds law enforcement agencies that there are concerns that Al Qaeda and other extremist groups may seek to influence or disrupt key events to include political conventions and the presidential election.

Security Precautions

The bulletin also describes suggested protective measures for government entities, security managers, subways and enclosed public spaces, personnel and computer networks. Many of the suggested security precautions are well known, such as increasing random inspection of backpacks and suitcases, increase foot patrols and approach all illegally parked vehicles around facilities.

Some of the more interesting security suggestions include:

—"Report any suspicious medical conditions of multiple personnel in subways/enclosed public spaces (e.g. shopping malls)."

—"Install special locking devices on manhole covers in and around facilities if feasible."

— Regarding computer networks, validate readiness of backup sites, brief computer security/incident response staff on current threat information and monitor network for abnormal activity.

FOX News' Catherine Herridge and Anna Stolley contributed to this report.